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rfc:rfc2898

Network Working Group B. Kaliski Request for Comments: 2898 RSA Laboratories Category: Informational September 2000

         PKCS #5: Password-Based Cryptography Specification
                            Version 2.0

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This memo represents a republication of PKCS #5 v2.0 from RSA
 Laboratories' Public-Key Cryptography Standards (PKCS) series, and
 change control is retained within the PKCS process.  The body of this
 document, except for the security considerations section, is taken
 directly from that specification.
 This document provides recommendations for the implementation of
 password-based cryptography, covering key derivation functions,
 encryption schemes, message-authentication schemes, and ASN.1 syntax
 identifying the techniques.
 The recommendations are intended for general application within
 computer and communications systems, and as such include a fair
 amount of flexibility. They are particularly intended for the
 protection of sensitive information such as private keys, as in PKCS
 #8 [25]. It is expected that application standards and implementation
 profiles based on these specifications may include additional
 constraints.
 Other cryptographic techniques based on passwords, such as password-
 based key entity authentication and key establishment protocols
 [4][5][26] are outside the scope of this document.  Guidelines for
 the selection of passwords are also outside the scope.

Kaliski Informational [Page 1] RFC 2898 Password-Based Cryptography September 2000

Table of Contents

 1.   Introduction ...............................................  3
 2.   Notation ...................................................  3
 3.   Overview ...................................................  4
 4.   Salt and iteration count ...................................  6
     4.1  Salt ...................................................  6
     4.2  Iteration count ........................................  8
 5.   Key derivation functions ...................................  8
     5.1  PBKDF1 .................................................  9
     5.2  PBKDF2 .................................................  9
 6.   Encryption schemes ......................................... 11
     6.1  PBES1 .................................................. 12
          6.1.1  Encryption operation ............................ 12
          6.1.2  Decryption operation ............................ 13
     6.2  PBES2 .................................................. 14
          6.2.1  Encryption operation ............................ 14
          6.2.2  Decryption operation ............................ 15
 7.   Message authentication schemes ............................. 15
     7.1  PBMAC1 ................................................. 16
          7.1.1  MAC generation .................................. 16
          7.1.2  MAC verification ................................ 16
 8.   Security Considerations .................................... 17
 9.   Author's Address............................................ 17
 A.   ASN.1 syntax ............................................... 18
     A.1  PBKDF1 ................................................. 18
     A.2  PBKDF2 ................................................. 18
     A.3  PBES1 .................................................. 20
     A.4  PBES2 .................................................. 20
     A.5  PBMAC1 ................................................. 21
 B.   Supporting techniques ...................................... 22
     B.1  Pseudorandom functions ................................. 22
     B.2  Encryption schemes ..................................... 23
     B.3  Message authentication schemes ......................... 26
 C.   ASN.1 module ............................................... 26
 Intellectual Property Considerations ............................ 30
 Revision history ................................................ 30
 References ...................................................... 31
 Contact Information & About PKCS ................................ 33
 Full Copyright Statement ........................................ 34

Kaliski Informational [Page 2] RFC 2898 Password-Based Cryptography September 2000

1. Introduction

 This document provides recommendations for the implementation of
 password-based cryptography, covering the following aspects:
  1. key derivation functions
  2. encryption schemes
  3. message-authentication schemes
  4. ASN.1 syntax identifying the techniques
 The recommendations are intended for general application within
 computer and communications systems, and as such include a fair
 amount of flexibility. They are particularly intended for the
 protection of sensitive information such as private keys, as in PKCS
 #8 [25]. It is expected that application standards and implementation
 profiles based on these specifications may include additional
 constraints.
 Other cryptographic techniques based on passwords, such as password-
 based key entity authentication and key establishment protocols
 [4][5][26] are outside the scope of this document.  Guidelines for
 the selection of passwords are also outside the scope.
 This document supersedes PKCS #5 version 1.5 [24], but includes
 compatible techniques.

2. Notation

 C       ciphertext, an octet string
 c       iteration count, a positive integer
 DK      derived key, an octet string
 dkLen   length in octets of derived key, a positive integer
 EM      encoded message, an octet string
 Hash    underlying hash function
 hLen    length in octets of pseudorandom function output, a positive
         integer
 l       length in blocks of derived key, a positive integer
 IV      initialization vector, an octet string
 K       encryption key, an octet string

Kaliski Informational [Page 3] RFC 2898 Password-Based Cryptography September 2000

 KDF     key derivation function
 M       message, an octet string
 P       password, an octet string
 PRF     underlying pseudorandom function
 PS      padding string, an octet string
 psLen   length in octets of padding string, a positive integer
 S       salt, an octet string
 T       message authentication code, an octet string
 T_1, ..., T_l, U_1, ..., U_c
         intermediate values, octet strings
 01, 02, ..., 08
         octets with value 1, 2, ..., 8
 \xor    bit-wise exclusive-or of two octet strings
 ||  ||  octet length operator
 ||      concatenation operator
 <i..j>  substring extraction operator: extracts octets i through j,
         0 <= i <= j

3. Overview

 In many applications of public-key cryptography, user security is
 ultimately dependent on one or more secret text values or passwords.
 Since a password is not directly applicable as a key to any
 conventional cryptosystem, however, some processing of the password
 is required to perform cryptographic operations with it. Moreover, as
 passwords are often chosen from a relatively small space, special
 care is required in that processing to defend against search attacks.
 A general approach to password-based cryptography, as described by
 Morris and Thompson [8] for the protection of password tables, is to
 combine a password with a salt to produce a key. The salt can be
 viewed as an index into a large set of keys derived from the
 password, and need not be kept secret. Although it may be possible
 for an opponent to construct a table of possible passwords (a so-
 called "dictionary attack"), constructing a table of possible keys

Kaliski Informational [Page 4] RFC 2898 Password-Based Cryptography September 2000

 will be difficult, since there will be many possible keys for each
 password.  An opponent will thus be limited to searching through
 passwords separately for each salt.
 Another approach to password-based cryptography is to construct key
 derivation techniques that are relatively expensive, thereby
 increasing the cost of exhaustive search. One way to do this is to
 include an iteration count in the key derivation technique,
 indicating how many times to iterate some underlying function by
 which keys are derived. A modest number of iterations, say 1000, is
 not likely to be a burden for legitimate parties when computing a
 key, but will be a significant burden for opponents.
 Salt and iteration count formed the basis for password-based
 encryption in PKCS #5 v1.5, and adopted here as well for the various
 cryptographic operations. Thus, password-based key derivation as
 defined here is a function of a password, a salt, and an iteration
 count, where the latter two quantities need not be kept secret.
 From a password-based key derivation function, it is straightforward
 to define password-based encryption and message authentication
 schemes. As in PKCS #5 v1.5, the password-based encryption schemes
 here are based on an underlying, conventional encryption scheme,
 where the key for the conventional scheme is derived from the
 password. Similarly, the password-based message authentication scheme
 is based on an underlying conventional scheme. This two-layered
 approach makes the password-based techniques modular in terms of the
 underlying techniques they can be based on.
 It is expected that the password-based key derivation functions may
 find other applications than just the encryption and message
 authentication schemes defined here. For instance, one might derive a
 set of keys with a single application of a key derivation function,
 rather than derive each key with a separate application of the
 function. The keys in the set would be obtained as substrings of the
 output of the key derivation function. This approach might be
 employed as part of key establishment in a session-oriented protocol.
 Another application is password checking, where the output of the key
 derivation function is stored (along with the salt and iteration
 count) for the purposes of subsequent verification of a password.
 Throughout this document, a password is considered to be an octet
 string of arbitrary length whose interpretation as a text string is
 unspecified. In the interest of interoperability, however, it is
 recommended that applications follow some common text encoding rules.
 ASCII and UTF-8 [27] are two possibilities. (ASCII is a subset of
 UTF-8.)

Kaliski Informational [Page 5] RFC 2898 Password-Based Cryptography September 2000

 Although the selection of passwords is outside the scope of this
 document, guidelines have been published [17] that may well be taken
 into account.

4. Salt and Iteration Count

 Inasmuch as salt and iteration count are central to the techniques
 defined in this document, some further discussion is warranted.

4.1 Salt

 A salt in password-based cryptography has traditionally served the
 purpose of producing a large set of keys corresponding to a given
 password, among which one is selected at random according to the
 salt. An individual key in the set is selected by applying a key
 derivation function KDF, as
                            DK = KDF (P, S)
 where DK is the derived key, P is the password, and S is the salt.
 This has two benefits:
    1. It is difficult for an opponent to precompute all the keys
       corresponding to a dictionary of passwords, or even the most
       likely keys. If the salt is 64 bits long, for instance, there
       will be as many as 2^64 keys for each password. An opponent is
       thus limited to searching for passwords after a password-based
       operation has been performed and the salt is known.
    2. It is unlikely that the same key will be selected twice.
       Again, if the salt is 64 bits long, the chance of "collision"
       between keys does not become significant until about 2^32 keys
       have been produced, according to the Birthday Paradox. This
       addresses some of the concerns about interactions between
       multiple uses of the same key, which may apply for some
       encryption and authentication techniques.
 In password-based encryption, the party encrypting a message can gain
 assurance that these benefits are realized simply by selecting a
 large and sufficiently random salt when deriving an encryption key
 from a password. A party generating a message authentication code can
 gain such assurance in a similar fashion.
 The party decrypting a message or verifying a message authentication
 code, however, cannot be sure that a salt supplied by another party
 has actually been generated at random. It is possible, for instance,
 that the salt may have been copied from another password-based
 operation, in an attempt to exploit interactions between multiple

Kaliski Informational [Page 6] RFC 2898 Password-Based Cryptography September 2000

 uses of the same key. For instance, suppose two legitimate parties
 exchange a encrypted message, where the encryption key is an 80-bit
 key derived from a shared password with some salt. An opponent could
 take the salt from that encryption and provide it to one of the
 parties as though it were for a 40-bit key. If the party reveals the
 result of decryption with the 40-bit key, the opponent may be able to
 solve for the 40-bit key. In the case that 40-bit key is the first
 half of the 80-bit key, the opponent can then readily solve for the
 remaining 40 bits of the 80-bit key.
 To defend against such attacks, either the interaction between
 multiple uses of the same key should be carefully analyzed, or the
 salt should contain data that explicitly distinguishes between
 different operations.  For instance, the salt might have an
 additional, non-random octet that specifies whether the derived key
 is for encryption, for message authentication, or for some other
 operation.
 Based on this, the following is recommended for salt selection:
    1. If there is no concern about interactions between multiple uses
       of the same key (or a prefix of that key) with the password-
       based encryption and authentication techniques supported for a
       given password, then the salt may be generated at random and
       need not be checked for a particular format by the party
       receiving the salt. It should be at least eight octets (64
       bits) long.
    2. Otherwise, the salt should contain data that explicitly
       distinguishes between different operations and different key
       lengths, in addition to a random part that is at least eight
       octets long, and this data should be checked or regenerated by
       the party receiving the salt. For instance, the salt could have
       an additional non-random octet that specifies the purpose of
       the derived key. Alternatively, it could be the encoding of a
       structure that specifies detailed information about the derived
       key, such as the encryption or authentication technique and a
       sequence number among the different keys derived from the
       password.  The particular format of the additional data is left
       to the application.
 Note. If a random number generator or pseudorandom generator is not
 available, a deterministic alternative for generating the salt (or
 the random part of it) is to apply a password-based key derivation
 function to the password and the message M to be processed. For
 instance, the salt could be computed with a key derivation function
 as S = KDF (P, M). This approach is not recommended if the message M

Kaliski Informational [Page 7] RFC 2898 Password-Based Cryptography September 2000

 is known to belong to a small message space (e.g., "Yes" or "No"),
 however, since then there will only be a small number of possible
 salts.

4.2 Iteration Count

 An iteration count has traditionally served the purpose of increasing
 the cost of producing keys from a password, thereby also increasing
 the difficulty of attack. For the methods in this document, a minimum
 of 1000 iterations is recommended. This will increase the cost of
 exhaustive search for passwords significantly, without a noticeable
 impact in the cost of deriving individual keys.

5. Key Derivation Functions

 A key derivation function produces a derived key from a base key and
 other parameters. In a password-based key derivation function, the
 base key is a password and the other parameters are a salt value and
 an iteration count, as outlined in Section 3.
 The primary application of the password-based key derivation
 functions defined here is in the encryption schemes in Section 6 and
 the message authentication scheme in Section 7. Other applications
 are certainly possible, hence the independent definition of these
 functions.
 Two functions are specified in this section: PBKDF1 and PBKDF2.
 PBKDF2 is recommended for new applications; PBKDF1 is included only
 for compatibility with existing applications, and is not recommended
 for new applications.
 A typical application of the key derivation functions defined here
 might include the following steps:
    1. Select a salt S and an iteration count c, as outlined in
       Section 4.
    2. Select a length in octets for the derived key, dkLen.
    3. Apply the key derivation function to the password, the salt,
       the iteration count and the key length to produce a derived
       key.
    4. Output the derived key.
 Any number of keys may be derived from a password by varying the
 salt, as described in Section 3.

Kaliski Informational [Page 8] RFC 2898 Password-Based Cryptography September 2000

5.1 PBKDF1

 PBKDF1 applies a hash function, which shall be MD2 [6], MD5 [19] or
 SHA-1 [18], to derive keys. The length of the derived key is bounded
 by the length of the hash function output, which is 16 octets for MD2
 and MD5 and 20 octets for SHA-1. PBKDF1 is compatible with the key
 derivation process in PKCS #5 v1.5.
 PBKDF1 is recommended only for compatibility with existing
 applications since the keys it produces may not be large enough for
 some applications.
 PBKDF1 (P, S, c, dkLen)
 Options:        Hash       underlying hash function
 Input:          P          password, an octet string
                 S          salt, an eight-octet string
                 c          iteration count, a positive integer
                 dkLen      intended length in octets of derived key,
                            a positive integer, at most 16 for MD2 or
                            MD5 and 20 for SHA-1
 Output:         DK         derived key, a dkLen-octet string
 Steps:
    1. If dkLen > 16 for MD2 and MD5, or dkLen > 20 for SHA-1, output
       "derived key too long" and stop.
    2. Apply the underlying hash function Hash for c iterations to the
       concatenation of the password P and the salt S, then extract
       the first dkLen octets to produce a derived key DK:
                 T_1 = Hash (P || S) ,
                 T_2 = Hash (T_1) ,
                 ...
                 T_c = Hash (T_{c-1}) ,
                 DK = Tc<0..dkLen-1>
    3. Output the derived key DK.

5.2 PBKDF2

 PBKDF2 applies a pseudorandom function (see Appendix B.1 for an
 example) to derive keys. The length of the derived key is essentially
 unbounded. (However, the maximum effective search space for the

Kaliski Informational [Page 9] RFC 2898 Password-Based Cryptography September 2000

 derived key may be limited by the structure of the underlying
 pseudorandom function. See Appendix B.1 for further discussion.)
 PBKDF2 is recommended for new applications.
 PBKDF2 (P, S, c, dkLen)
 Options:        PRF        underlying pseudorandom function (hLen
                            denotes the length in octets of the
                            pseudorandom function output)
 Input:          P          password, an octet string
                 S          salt, an octet string
                 c          iteration count, a positive integer
                 dkLen      intended length in octets of the derived
                            key, a positive integer, at most
                            (2^32 - 1) * hLen
 Output:         DK         derived key, a dkLen-octet string
 Steps:
    1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and
       stop.
    2. Let l be the number of hLen-octet blocks in the derived key,
       rounding up, and let r be the number of octets in the last
       block:
                 l = CEIL (dkLen / hLen) ,
                 r = dkLen - (l - 1) * hLen .
       Here, CEIL (x) is the "ceiling" function, i.e. the smallest
       integer greater than, or equal to, x.
    3. For each block of the derived key apply the function F defined
       below to the password P, the salt S, the iteration count c, and
       the block index to compute the block:
                 T_1 = F (P, S, c, 1) ,
                 T_2 = F (P, S, c, 2) ,
                 ...
                 T_l = F (P, S, c, l) ,
       where the function F is defined as the exclusive-or sum of the
       first c iterates of the underlying pseudorandom function PRF
       applied to the password P and the concatenation of the salt S
       and the block index i:

Kaliski Informational [Page 10] RFC 2898 Password-Based Cryptography September 2000

                 F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
       where
                 U_1 = PRF (P, S || INT (i)) ,
                 U_2 = PRF (P, U_1) ,
                 ...
                 U_c = PRF (P, U_{c-1}) .
       Here, INT (i) is a four-octet encoding of the integer i, most
       significant octet first.
    4. Concatenate the blocks and extract the first dkLen octets to
       produce a derived key DK:
                 DK = T_1 || T_2 ||  ...  || T_l<0..r-1>
    5. Output the derived key DK.
 Note. The construction of the function F follows a "belt-and-
 suspenders" approach. The iterates U_i are computed recursively to
 remove a degree of parallelism from an opponent; they are exclusive-
 ored together to reduce concerns about the recursion degenerating
 into a small set of values.

6. Encryption Schemes

 An encryption scheme, in the symmetric setting, consists of an
 encryption operation and a decryption operation, where the encryption
 operation produces a ciphertext from a message under a key, and the
 decryption operation recovers the message from the ciphertext under
 the same key. In a password-based encryption scheme, the key is a
 password.
 A typical application of a password-based encryption scheme is a
 private-key protection method, where the message contains private-key
 information, as in PKCS #8. The encryption schemes defined here would
 be suitable encryption algorithms in that context.
 Two schemes are specified in this section: PBES1 and PBES2. PBES2 is
 recommended for new applications; PBES1 is included only for
 compatibility with existing applications, and is not recommended for
 new applications.

Kaliski Informational [Page 11] RFC 2898 Password-Based Cryptography September 2000

6.1 PBES1

 PBES1 combines the PBKDF1 function (Section 5.1) with an underlying
 block cipher, which shall be either DES [15] or RC2(tm) [21] in CBC
 mode [16]. PBES1 is compatible with the encryption scheme in PKCS #5
 v1.5.
 PBES1 is recommended only for compatibility with existing
 applications, since it supports only two underlying encryption
 schemes, each of which has a key size (56 or 64 bits) that may not be
 large enough for some applications.

6.1.1 Encryption Operation

 The encryption operation for PBES1 consists of the following steps,
 which encrypt a message M under a password P to produce a ciphertext
 C:
    1. Select an eight-octet salt S and an iteration count c, as
       outlined in Section 4.
    2. Apply the PBKDF1 key derivation function (Section 5.1) to the
       password P, the salt S, and the iteration count c to produce at
       derived key DK of length 16 octets:
               DK = PBKDF1 (P, S, c, 16) .
    3. Separate the derived key DK into an encryption key K consisting
       of the first eight octets of DK and an initialization vector IV
       consisting of the next eight octets:
               K   = DK<0..7> ,
               IV  = DK<8..15> .
    4. Concatenate M and a padding string PS to form an encoded
       message EM:
               EM = M || PS ,
       where the padding string PS consists of 8-(||M|| mod 8) octets
       each with value 8-(||M|| mod 8). The padding string PS will
       satisfy one of the following statements:
               PS = 01, if ||M|| mod 8 = 7 ;
               PS = 02 02, if ||M|| mod 8 = 6 ;
               ...
               PS = 08 08 08 08 08 08 08 08, if ||M|| mod 8 = 0.

Kaliski Informational [Page 12] RFC 2898 Password-Based Cryptography September 2000

       The length in octets of the encoded message will be a multiple
       of eight and it will be possible to recover the message M
       unambiguously from the encoded message. (This padding rule is
       taken from RFC 1423 [3].)
    5. Encrypt the encoded message EM with the underlying block cipher
       (DES or RC2) in cipher block chaining mode under the encryption
       key K with initialization vector IV to produce the ciphertext
       C. For DES, the key K shall be considered as a 64-bit encoding
       of a 56-bit DES key with parity bits ignored (see [9]). For
       RC2, the "effective key bits" shall be 64 bits.
    6.   Output the ciphertext C.
 The salt S and the iteration count c may be conveyed to the party
 performing decryption in an AlgorithmIdentifier value (see Appendix
 A.3).

6.1.2 Decryption Operation

 The decryption operation for PBES1 consists of the following steps,
 which decrypt a ciphertext C under a password P to recover a message
 M:
    1. Obtain the eight-octet salt S and the iteration count c.
    2. Apply the PBKDF1 key derivation function (Section 5.1) to the
       password P, the salt S, and the iteration count c to produce a
       derived key DK of length 16 octets:
               DK = PBKDF1 (P, S, c, 16)
    3. Separate the derived key DK into an encryption key K consisting
       of the first eight octets of DK and an initialization vector IV
       consisting of the next eight octets:
               K = DK<0..7> ,
               IV  = DK<8..15> .
    4. Decrypt the ciphertext C with the underlying block cipher (DES
       or RC2) in cipher block chaining mode under the encryption key
       K with initialization vector IV to recover an encoded message
       EM. If the length in octets of the ciphertext C is not a
       multiple of eight, output "decryption error" and stop.
    5. Separate the encoded message EM into a message M and a padding
       string PS:

Kaliski Informational [Page 13] RFC 2898 Password-Based Cryptography September 2000

               EM = M || PS ,
       where the padding string PS consists of some number psLen
       octets each with value psLen, where psLen is between 1 and 8.
       If it is not possible to separate the encoded message EM in
       this manner, output "decryption error" and stop.
    6. Output the recovered message M.

6.2 PBES2

 PBES2 combines a password-based key derivation function, which shall
 be PBKDF2 (Section 5.2) for this version of PKCS #5, with an
 underlying encryption scheme (see Appendix B.2 for examples). The key
 length and any other parameters for the underlying encryption scheme
 depend on the scheme.
 PBES2 is recommended for new applications.

6.2.1 Encryption Operation

 The encryption operation for PBES2 consists of the following steps,
 which encrypt a message M under a password P to produce a ciphertext
 C, applying a selected key derivation function KDF and a selected
 underlying encryption scheme:
    1. Select a salt S and an iteration count c, as outlined in
       Section 4.
    2. Select the length in octets, dkLen, for the derived key for the
       underlying encryption scheme.
    3. Apply the selected key derivation function to the password P,
       the salt S, and the iteration count c to produce a derived key
       DK of length dkLen octets:
               DK = KDF (P, S, c, dkLen) .
    4. Encrypt the message M with the underlying encryption scheme
       under the derived key DK to produce a ciphertext C. (This step
       may involve selection of parameters such as an initialization
       vector and padding, depending on the underlying scheme.)
    5. Output the ciphertext C.

Kaliski Informational [Page 14] RFC 2898 Password-Based Cryptography September 2000

 The salt S, the iteration count c, the key length dkLen, and
 identifiers for the key derivation function and the underlying
 encryption scheme may be conveyed to the party performing decryption
 in an AlgorithmIdentifier value (see Appendix A.4).

6.2.2 Decryption Operation

 The decryption operation for PBES2 consists of the following steps,
 which decrypt a ciphertext C under a password P to recover a message
 M:
    1. Obtain the salt S for the operation.
    2. Obtain the iteration count c for the key derivation function.
    3. Obtain the key length in octets, dkLen, for the derived key for
       the underlying encryption scheme.
    4. Apply the selected key derivation function to the password P,
       the salt S, and the iteration count c to produce a derived key
       DK of length dkLen octets:
               DK = KDF (P, S, c, dkLen) .
    5. Decrypt the ciphertext C with the underlying encryption scheme
       under the derived key DK to recover a message M. If the
       decryption function outputs "decryption error," then output
       "decryption error" and stop.
    6. Output the recovered message M.

7. Message Authentication Schemes

 A message authentication scheme consists of a MAC (message
 authentication code) generation operation and a MAC verification
 operation, where the MAC generation operation produces a message
 authentication code from a message under a key, and the MAC
 verification operation verifies the message authentication code under
 the same key. In a password-based message authentication scheme, the
 key is a password.
 One scheme is specified in this section: PBMAC1.

Kaliski Informational [Page 15] RFC 2898 Password-Based Cryptography September 2000

7.1 PBMAC1

 PBMAC1 combines a password-based key derivation function, which shall
 be PBKDF2  (Section 5.2) for this version of PKCS #5, with an
 underlying message authentication scheme (see Appendix B.3 for an
 example). The key length and any other parameters for the underlying
 message authentication scheme depend on the scheme.

7.1.1 MAC Generation

 The MAC generation operation for PBMAC1 consists of the following
 steps, which process a message M under a password P to generate a
 message authentication code T, applying a selected key derivation
 function KDF and a selected underlying message authentication scheme:
    1. Select a salt S and an iteration count c, as outlined in
       Section 4.
    2. Select a key length in octets, dkLen, for the derived key for
       the underlying message authentication function.
    3. Apply the selected key derivation function to the password P,
       the salt S, and the iteration count c to produce a derived key
       DK of length dkLen octets:
               DK = KDF (P, S, c, dkLen) .
    4. Process the message M with the underlying message
       authentication scheme under the derived key DK to generate a
       message authentication code T.
    5. Output the message authentication code T.
 The salt S, the iteration count c, the key length dkLen, and
 identifiers for the key derivation function and underlying message
 authentication scheme may be conveyed to the party performing
 verification in an AlgorithmIdentifier value (see Appendix A.5).

7.1.2 MAC Verification

 The MAC verification operation for PBMAC1 consists of the following
 steps, which process a message M under a password P to verify a
 message authentication code T:
    1. Obtain the salt S and the iteration count c.
    2. Obtain the key length in octets, dkLen, for the derived key for
       the underlying message authentication scheme.

Kaliski Informational [Page 16] RFC 2898 Password-Based Cryptography September 2000

    3. Apply the selected key derivation function to the password P,
       the salt S, and the iteration count c to produce a derived key
       DK of length dkLen octets:
               DK = KDF (P, S, c, dkLen) .
    4. Process the message M with the underlying message
       authentication scheme under the derived key DK to verify the
       message authentication code T.
    5. If the message authentication code verifies, output "correct";
       else output "incorrect."

8. Security Considerations

 Password-based cryptography is generally limited in the security that
 it can provide, particularly for methods such as those defined in
 this document where off-line password search is possible. While the
 use of salt and iteration count can increase the complexity of attack
 (see Section 4 for recommendations), it is essential that passwords
 are selected well, and relevant guidelines (e.g., [17]) should be
 taken into account. It is also important that passwords be protected
 well if stored.
 In general, different keys should be derived from a password for
 different uses to minimize the possibility of unintended
 interactions. For password-based encryption with a single algorithm,
 a random salt is sufficient to ensure that different keys will be
 produced. In certain other situations, as outlined in Section 4, a
 structured salt is necessary. The recommendations in Section 4 should
 thus be taken into account when selecting the salt value.

9. Author's Address

 Burt Kaliski
 RSA Laboratories
 20 Crosby Drive
 Bedford, MA 01730 USA
 EMail: bkaliski@rsasecurity.com

Kaliski Informational [Page 17] RFC 2898 Password-Based Cryptography September 2000

APPENDICES

A. ASN.1 Syntax

 This section defines ASN.1 syntax for the key derivation functions,
 the encryption schemes, the message authentication scheme, and
 supporting techniques. The intended application of these definitions
 includes PKCS #8 and other syntax for key management, encrypted data,
 and integrity-protected data. (Various aspects of ASN.1 are specified
 in several ISO/IEC standards [9][10][11][12][13][14].)
 The object identifier pkcs-5 identifies the arc of the OID tree from
 which the PKCS #5-specific OIDs in this section are derived:
 rsadsi OBJECT IDENTIFIER ::= {iso(1) member-body(2) us(840) 113549}
 pkcs OBJECT IDENTIFIER   ::= {rsadsi 1}
 pkcs-5 OBJECT IDENTIFIER ::= {pkcs 5}

A.1 PBKDF1

 No object identifier is given for PBKDF1, as the object identifiers
 for PBES1 are sufficient for existing applications and PBKDF2 is
 recommended for new applications.

A.2 PBKDF2

 The object identifier id-PBKDF2 identifies the PBKDF2 key derivation
 function (Section 5.2).
 id-PBKDF2 OBJECT IDENTIFIER ::= {pkcs-5 12}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type PBKDF2-params:
 PBKDF2-params ::= SEQUENCE {
     salt CHOICE {
         specified OCTET STRING,
         otherSource AlgorithmIdentifier {{PBKDF2-SaltSources}}
     },
     iterationCount INTEGER (1..MAX),
     keyLength INTEGER (1..MAX) OPTIONAL,
     prf AlgorithmIdentifier {{PBKDF2-PRFs}} DEFAULT
     algid-hmacWithSHA1 }
 The fields of type PKDF2-params have the following meanings:

Kaliski Informational [Page 18] RFC 2898 Password-Based Cryptography September 2000

  1. salt specifies the salt value, or the source of the salt value.

It shall either be an octet string or an algorithm ID with an OID

    in the set PBKDF2-SaltSources, which is reserved for future
    versions of PKCS #5.
    The salt-source approach is intended to indicate how the salt
    value is to be generated as a function of parameters in the
    algorithm ID, application data, or both. For instance, it may
    indicate that the salt value is produced from the encoding of a
    structure that specifies detailed information about the derived
    key as suggested in Section 4.1. Some of the information may be
    carried elsewhere, e.g., in the encryption algorithm ID. However,
    such facilities are deferred to a future version of PKCS #5.
    In this version, an application may achieve the benefits mentioned
    in Section 4.1 by choosing a particular interpretation of the salt
    value in the specified alternative.
 PBKDF2-SaltSources ALGORITHM-IDENTIFIER ::= { ... }
  1. iterationCount specifies the iteration count. The maximum

iteration count allowed depends on the implementation. It is

    expected that implementation profiles may further constrain the
    bounds.
  1. keyLength, an optional field, is the length in octets of the

derived key. The maximum key length allowed depends on the

    implementation; it is expected that implementation profiles may
    further constrain the bounds. The field is provided for
    convenience only; the key length is not cryptographically
    protected. If there is concern about interaction between
    operations with different key lengths for a given salt (see
    Section 4.1), the salt should distinguish among the different key
    lengths.
  1. prf identifies the underlying pseudorandom function. It shall be

an algorithm ID with an OID in the set PBKDF2-PRFs, which for this

    version of PKCS #5 shall consist of id-hmacWithSHA1 (see Appendix
    B.1.1) and any other OIDs defined by the application.
    PBKDF2-PRFs ALGORITHM-IDENTIFIER ::=
        { {NULL IDENTIFIED BY id-hmacWithSHA1}, ... }
    The default pseudorandom function is HMAC-SHA-1:
    algid-hmacWithSHA1 AlgorithmIdentifier {{PBKDF2-PRFs}} ::=
        {algorithm id-hmacWithSHA1, parameters NULL : NULL}

Kaliski Informational [Page 19] RFC 2898 Password-Based Cryptography September 2000

A.3 PBES1

 Different object identifiers identify the PBES1 encryption scheme
 (Section 6.1) according to the underlying hash function in the key
 derivation function and the underlying block cipher, as summarized in
 the following table:
      Hash Function  Block Cipher      OID
           MD2           DES         pkcs-5.1
           MD2           RC2         pkcs-5.4
           MD5           DES         pkcs-5.3
           MD5           RC2         pkcs-5.6
          SHA-1          DES         pkcs-5.10
          SHA-1          RC2         pkcs-5.11
 pbeWithMD2AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 1}
 pbeWithMD2AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 4}
 pbeWithMD5AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 3}
 pbeWithMD5AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 6}
 pbeWithSHA1AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 10}
 pbeWithSHA1AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 11}
 For each OID, the parameters field associated with the OID in an
 AlgorithmIdentifier shall have type PBEParameter:
 PBEParameter ::= SEQUENCE {
     salt OCTET STRING (SIZE(8)),
     iterationCount INTEGER }
 The fields of type PBEParameter have the following meanings:
  1. salt specifies the salt value, an eight-octet string.
  1. iterationCount specifies the iteration count.

A.4 PBES2

 The object identifier id-PBES2 identifies the PBES2 encryption scheme
 (Section 6.2).
 id-PBES2 OBJECT IDENTIFIER ::= {pkcs-5 13}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type PBES2-params:
 PBES2-params ::= SEQUENCE {
     keyDerivationFunc AlgorithmIdentifier {{PBES2-KDFs}},
     encryptionScheme AlgorithmIdentifier {{PBES2-Encs}} }

Kaliski Informational [Page 20] RFC 2898 Password-Based Cryptography September 2000

 The fields of type PBES2-params have the following meanings:
  1. keyDerivationFunc identifies the underlying key derivation

function. It shall be an algorithm ID with an OID in the set

    PBES2-KDFs, which for this version of PKCS #5 shall consist of
    id-PBKDF2 (Appendix A.2).
 PBES2-KDFs ALGORITHM-IDENTIFIER ::=
     { {PBKDF2-params IDENTIFIED BY id-PBKDF2}, ... }
  1. encryptionScheme identifies the underlying encryption scheme. It

shall be an algorithm ID with an OID in the set PBES2-Encs, whose

    definition is left to the application. Example underlying
    encryption schemes are given in Appendix B.2.
 PBES2-Encs ALGORITHM-IDENTIFIER ::= { ... }

A.5 PBMAC1

 The object identifier id-PBMAC1 identifies the PBMAC1 message
 authentication scheme (Section 7.1).
 id-PBMAC1 OBJECT IDENTIFIER ::= {pkcs-5 14}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type PBMAC1-params:
 PBMAC1-params ::=  SEQUENCE {
     keyDerivationFunc AlgorithmIdentifier {{PBMAC1-KDFs}},
     messageAuthScheme AlgorithmIdentifier {{PBMAC1-MACs}} }
 The keyDerivationFunc field has the same meaning as the corresponding
 field of PBES2-params (Appendix A.4) except that the set of OIDs is
 PBMAC1-KDFs.
 PBMAC1-KDFs ALGORITHM-IDENTIFIER ::=
     { {PBKDF2-params IDENTIFIED BY id-PBKDF2}, ... }
 The messageAuthScheme field identifies the underlying message
 authentication scheme. It shall be an algorithm ID with an OID in the
 set PBMAC1-MACs, whose definition is left to the application. Example
 underlying encryption schemes are given in Appendix B.3.
 PBMAC1-MACs ALGORITHM-IDENTIFIER ::= { ... }

Kaliski Informational [Page 21] RFC 2898 Password-Based Cryptography September 2000

B. Supporting Techniques

 This section gives several examples of underlying functions and
 schemes supporting the password-based schemes in Sections 5, 6 and 7.
 While these supporting techniques are appropriate for applications to
 implement, none of them is required to be implemented. It is
 expected, however, that profiles for PKCS #5 will be developed that
 specify particular supporting techniques.
 This section also gives object identifiers for the supporting
 techniques.  The object identifiers digestAlgorithm and
 encryptionAlgorithm identify the arcs from which certain algorithm
 OIDs referenced in this section are derived:
 digestAlgorithm OBJECT IDENTIFIER ::= {rsadsi 2}
 encryptionAlgorithm OBJECT IDENTIFIER ::= {rsadsi 3}

B.1 Pseudorandom functions

 An example pseudorandom function for PBKDF2 (Section 5.2) is HMAC-
 SHA-1.

B.1.1 HMAC-SHA-1

 HMAC-SHA-1 is the pseudorandom function corresponding to the HMAC
 message authentication code [7] based on the SHA-1 hash function
 [18].  The pseudorandom function is the same function by which the
 message authentication code is computed, with a full-length output.
 (The first argument to the pseudorandom function PRF serves as HMAC's
 "key," and the second serves as HMAC's "text." In the case of PBKDF2,
 the "key" is thus the password and the "text" is the salt.)  HMAC-
 SHA-1 has a variable key length and a 20-octet (160-bit) output
 value.
 Although the length of the key to HMAC-SHA-1 is essentially
 unbounded, the effective search space for pseudorandom function
 outputs may be limited by the structure of the function. In
 particular, when the key is longer than 512 bits, HMAC-SHA-1 will
 first hash it to 160 bits. Thus, even if a long derived key
 consisting of several pseudorandom function outputs is produced from
 a key, the effective search space for the derived key will be at most
 160 bits. Although the specific limitation for other key sizes
 depends on details of the HMAC construction, one should assume, to be
 conservative, that the effective search space is limited to 160 bits
 for other key sizes as well.

Kaliski Informational [Page 22] RFC 2898 Password-Based Cryptography September 2000

 (The 160-bit limitation should not generally pose a practical
 limitation in the case of password-based cryptography, since the
 search space for a password is unlikely to be greater than 160 bits.)
 The object identifier id-hmacWithSHA1 identifies the HMAC-SHA-1
 pseudorandom function:
 id-hmacWithSHA1 OBJECT IDENTIFIER ::= {digestAlgorithm 7}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type NULL. This object identifier is
 employed in the object set PBKDF2-PRFs (Appendix A.2).
 Note. Although HMAC-SHA-1 was designed as a message authentication
 code, its proof of security is readily modified to accommodate
 requirements for a pseudorandom function, under stronger assumptions.
 A hash function may also meet the requirements of a pseudorandom
 function under certain assumptions. For instance, the direct
 application of a hash function to to the concatenation of the "key"
 and the "text" may be appropriate, provided that "text" has
 appropriate structure to prevent certain attacks. HMAC-SHA-1 is
 preferable, however, because it treats "key" and "text" as separate
 arguments and does not require "text" to have any structure.

B.2 Encryption Schemes

 Example pseudorandom functions for PBES2 (Section 6.2) are DES-CBC-
 Pad, DES-EDE2-CBC-Pad, RC2-CBC-Pad, and RC5-CBC-Pad.
 The object identifiers given in this section are intended to be
 employed in the object set PBES2-Encs (Appendix A.4).

B.2.1 DES-CBC-Pad

 DES-CBC-Pad is single-key DES [15] in CBC mode [16] with the RFC 1423
 padding operation (see Section 6.1.1). DES-CBC-Pad has an eight-octet
 encryption key and an eight-octet initialization vector.  The key is
 considered as a 64-bit encoding of a 56-bit DES key with parity bits
 ignored.
 The object identifier desCBC (defined in the NIST/OSI Implementors'
 Workshop agreements) identifies the DES-CBC-Pad encryption scheme:
 desCBC OBJECT IDENTIFIER ::=
     {iso(1) identified-organization(3) oiw(14) secsig(3)
      algorithms(2) 7}

Kaliski Informational [Page 23] RFC 2898 Password-Based Cryptography September 2000

 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type OCTET STRING (SIZE(8)),
 specifying the initialization vector for CBC mode.

B.2.2 DES-EDE3-CBC-Pad

 DES-EDE3-CBC-Pad is three-key triple-DES in CBC mode [1] with the RFC
 1423 padding operation. DES-EDE3-CBC-Pad has a 24-octet encryption
 key and an eight-octet initialization vector. The key is considered
 as the concatenation of three eight-octet keys, each of which is a
 64-bit encoding of a 56-bit DES key with parity bits ignored.
 The object identifier des-EDE3-CBC identifies the DES-EDE3-CBC-Pad
 encryption scheme:
 des-EDE3-CBC OBJECT IDENTIFIER ::= {encryptionAlgorithm 7}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type OCTET STRING (SIZE(8)),
 specifying the initialization vector for CBC mode.
 Note. An OID for DES-EDE3-CBC without padding is given in ANSI X9.52
 [1]; the one given here is preferred since it specifies padding.

B.2.3 RC2-CBC-Pad

 RC2-CBC-Pad is the RC2(tm) encryption algorithm [21] in CBC mode with
 the RFC 1423 padding operation. RC2-CBC-Pad has a variable key
 length, from one to 128 octets, a separate "effective key bits"
 parameter from one to 1024 bits that limits the effective search
 space independent of the key length, and an eight-octet
 initialization vector.
 The object identifier rc2CBC identifies the RC2-CBC-Pad encryption
 scheme:
 rc2CBC OBJECT IDENTIFIER ::= {encryptionAlgorithm 2}
 The parameters field associated with OID in an AlgorithmIdentifier
 shall have type RC2-CBC-Parameter:
 RC2-CBC-Parameter ::= SEQUENCE {
     rc2ParameterVersion INTEGER OPTIONAL,
     iv OCTET STRING (SIZE(8)) }

Kaliski Informational [Page 24] RFC 2898 Password-Based Cryptography September 2000

 The fields of type RC2-CBCParameter have the following meanings:
  1. rc2ParameterVersion is a proprietary RSA Security Inc. encoding of

the "effective key bits" for RC2. The following encodings are

    defined:
       Effective Key Bits         Encoding
               40                    160
               64                    120
              128                     58
             b >= 256                  b
 If the rc2ParameterVersion field is omitted, the "effective key bits"
 defaults to 32. (This is for backward compatibility with certain very
 old implementations.)
  1. iv is the eight-octet initialization vector.

B.2.4 RC5-CBC-Pad

 RC5-CBC-Pad is the RC5(tm) encryption algorithm [20] in CBC mode with
 a generalization of the RFC 1423 padding operation. This scheme is
 fully specified in [2]. RC5-CBC-Pad has a variable key length, from 0
 to 256 octets, and supports both a 64-bit block size and a 128-bit
 block size. For the former, it has an eight-octet initialization
 vector, and for the latter, a 16-octet initialization vector.
 RC5-CBC-Pad also has a variable number of "rounds" in the encryption
 operation, from 8 to 127.
 Note: The generalization of the padding operation is as follows. For
 RC5 with a 64-bit block size, the padding string is as defined in RFC
 1423. For RC5 with a 128-bit block size, the padding string consists
 of 16-(||M|| mod 16) octets each with value 16-(||M|| mod 16).
 The object identifier rc5-CBC-PAD [2] identifies RC5-CBC-Pad
 encryption scheme:
 rc5-CBC-PAD OBJECT IDENTIFIER ::= {encryptionAlgorithm 9}
 The parameters field associated with this OID in an
 AlgorithmIdentifier shall have type RC5-CBC-Parameters:
 RC5-CBC-Parameters ::= SEQUENCE {
     version INTEGER {v1-0(16)} (v1-0),
     rounds INTEGER (8..127),
     blockSizeInBits INTEGER (64 | 128),
     iv OCTET STRING OPTIONAL }

Kaliski Informational [Page 25] RFC 2898 Password-Based Cryptography September 2000

 The fields of type RC5-CBC-Parameters have the following meanings:
  1. version is the version of the algorithm, which shall be v1-0.
  1. rounds is the number of rounds in the encryption operation, which

shall be between 8 and 127.

  1. blockSizeInBits is the block size in bits, which shall be 64 or

128.

  1. iv is the initialization vector, an eight-octet string for 64-bit

RC5 and a 16-octet string for 128-bit RC5. The default is a string

    of the appropriate length consisting of zero octets.

B.3 Message Authentication Schemes

 An example message authentication scheme for PBMAC1 (Section 7.1) is
 HMAC-SHA-1.

B.3.1 HMAC-SHA-1

 HMAC-SHA-1 is the HMAC message authentication scheme [7] based on the
 SHA-1 hash function [18]. HMAC-SHA-1 has a variable key length and a
 20-octet (160-bit) message authentication code.
 The object identifier id-hmacWithSHA1 (see Appendix B.1.1) identifies
 the HMAC-SHA-1 message authentication scheme. (The object identifier
 is the same for both the pseudorandom function and the message
 authentication scheme; the distinction is to be understood by
 context.) This object identifier is intended to be employed in the
 object set PBMAC1-Macs (Appendix A.5).

C. ASN.1 Module

 For reference purposes, the ASN.1 syntax in the preceding sections is
 presented as an ASN.1 module here.
  1. - PKCS #5 v2.0 ASN.1 Module
  2. - Revised March 25, 1999
  1. - This module has been checked for conformance with the
  2. - ASN.1 standard by the OSS ASN.1 Tools
 PKCS5v2-0 {iso(1) member-body(2) us(840) rsadsi(113549)
     pkcs(1) pkcs-5(5) modules(16) pkcs5v2-0(1)}
 DEFINITIONS ::= BEGIN

Kaliski Informational [Page 26] RFC 2898 Password-Based Cryptography September 2000

  1. - Basic object identifiers
 rsadsi OBJECT IDENTIFIER ::= {iso(1) member-body(2) us(840) 113549}
 pkcs OBJECT IDENTIFIER ::= {rsadsi 1}
 pkcs-5 OBJECT IDENTIFIER ::= {pkcs 5}
  1. - Basic types and classes
 AlgorithmIdentifier { ALGORITHM-IDENTIFIER:InfoObjectSet } ::=
   SEQUENCE {
     algorithm ALGORITHM-IDENTIFIER.&id({InfoObjectSet}),
     parameters ALGORITHM-IDENTIFIER.&Type({InfoObjectSet}
     {@algorithm}) OPTIONAL
 }
 ALGORITHM-IDENTIFIER ::= TYPE-IDENTIFIER
  1. - PBKDF2
 PBKDF2Algorithms ALGORITHM-IDENTIFIER ::=
     { {PBKDF2-params IDENTIFIED BY id-PBKDF2}, ...}
 id-PBKDF2 OBJECT IDENTIFIER ::= {pkcs-5 12}
 algid-hmacWithSHA1 AlgorithmIdentifier {{PBKDF2-PRFs}} ::=
     {algorithm id-hmacWithSHA1, parameters NULL : NULL}
 PBKDF2-params ::= SEQUENCE {
     salt CHOICE {
       specified OCTET STRING,
       otherSource AlgorithmIdentifier {{PBKDF2-SaltSources}}
     },
     iterationCount INTEGER (1..MAX),
     keyLength INTEGER (1..MAX) OPTIONAL,
     prf AlgorithmIdentifier {{PBKDF2-PRFs}} DEFAULT
     algid-hmacWithSHA1
 }
 PBKDF2-SaltSources ALGORITHM-IDENTIFIER ::= { ... }
 PBKDF2-PRFs ALGORITHM-IDENTIFIER ::=
     { {NULL IDENTIFIED BY id-hmacWithSHA1}, ... }
  1. - PBES1
 PBES1Algorithms ALGORITHM-IDENTIFIER ::= {

Kaliski Informational [Page 27] RFC 2898 Password-Based Cryptography September 2000

     {PBEParameter IDENTIFIED BY pbeWithMD2AndDES-CBC}  |
     {PBEParameter IDENTIFIED BY pbeWithMD2AndRC2-CBC}  |
     {PBEParameter IDENTIFIED BY pbeWithMD5AndDES-CBC}  |
     {PBEParameter IDENTIFIED BY pbeWithMD5AndRC2-CBC}  |
     {PBEParameter IDENTIFIED BY pbeWithSHA1AndDES-CBC} |
     {PBEParameter IDENTIFIED BY pbeWithSHA1AndRC2-CBC},
     ...
 }
 pbeWithMD2AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 1}
 pbeWithMD2AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 4}
 pbeWithMD5AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 3}
 pbeWithMD5AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 6}
 pbeWithSHA1AndDES-CBC OBJECT IDENTIFIER ::= {pkcs-5 10}
 pbeWithSHA1AndRC2-CBC OBJECT IDENTIFIER ::= {pkcs-5 11}
 PBEParameter ::= SEQUENCE {
     salt OCTET STRING (SIZE(8)),
     iterationCount INTEGER
 }
  1. - PBES2
 PBES2Algorithms ALGORITHM-IDENTIFIER ::=
     { {PBES2-params IDENTIFIED BY id-PBES2}, ...}
 id-PBES2 OBJECT IDENTIFIER ::= {pkcs-5 13}
 PBES2-params ::= SEQUENCE {
     keyDerivationFunc AlgorithmIdentifier {{PBES2-KDFs}},
     encryptionScheme AlgorithmIdentifier {{PBES2-Encs}}
 }
 PBES2-KDFs ALGORITHM-IDENTIFIER ::=
     { {PBKDF2-params IDENTIFIED BY id-PBKDF2}, ... }
 PBES2-Encs ALGORITHM-IDENTIFIER ::= { ... }
  1. - PBMAC1
 PBMAC1Algorithms ALGORITHM-IDENTIFIER ::=
     { {PBMAC1-params IDENTIFIED BY id-PBMAC1}, ...}
 id-PBMAC1 OBJECT IDENTIFIER ::= {pkcs-5 14}
 PBMAC1-params ::=  SEQUENCE {
     keyDerivationFunc AlgorithmIdentifier {{PBMAC1-KDFs}},
     messageAuthScheme AlgorithmIdentifier {{PBMAC1-MACs}}

Kaliski Informational [Page 28] RFC 2898 Password-Based Cryptography September 2000

 }
 PBMAC1-KDFs ALGORITHM-IDENTIFIER ::=
     { {PBKDF2-params IDENTIFIED BY id-PBKDF2}, ... }
 PBMAC1-MACs ALGORITHM-IDENTIFIER ::= { ... }
  1. - Supporting techniques
 digestAlgorithm OBJECT IDENTIFIER     ::= {rsadsi 2}
 encryptionAlgorithm OBJECT IDENTIFIER ::= {rsadsi 3}
 SupportingAlgorithms ALGORITHM-IDENTIFIER ::= {
     {NULL IDENTIFIED BY id-hmacWithSHA1} |
     {OCTET STRING (SIZE(8)) IDENTIFIED BY desCBC} |
     {OCTET STRING (SIZE(8)) IDENTIFIED BY des-EDE3-CBC} |
     {RC2-CBC-Parameter IDENTIFIED BY rc2CBC} |
     {RC5-CBC-Parameters IDENTIFIED BY rc5-CBC-PAD},
     ...
 }
 id-hmacWithSHA1 OBJECT IDENTIFIER ::= {digestAlgorithm 7}
 desCBC OBJECT IDENTIFIER ::=
     {iso(1) identified-organization(3) oiw(14) secsig(3)
      algorithms(2) 7} -- from OIW
 des-EDE3-CBC OBJECT IDENTIFIER ::= {encryptionAlgorithm 7}
 rc2CBC OBJECT IDENTIFIER ::= {encryptionAlgorithm 2}
 RC2-CBC-Parameter ::= SEQUENCE {
     rc2ParameterVersion INTEGER OPTIONAL,
     iv OCTET STRING (SIZE(8))
 }
 rc5-CBC-PAD OBJECT IDENTIFIER ::= {encryptionAlgorithm 9}
 RC5-CBC-Parameters ::= SEQUENCE {
     version INTEGER {v1-0(16)} (v1-0),
     rounds INTEGER (8..127),
     blockSizeInBits INTEGER (64 | 128),
     iv OCTET STRING OPTIONAL
 }
 END

Kaliski Informational [Page 29] RFC 2898 Password-Based Cryptography September 2000

Intellectual Property Considerations

 RSA Security makes no patent claims on the general constructions
 described in this document, although specific underlying techniques
 may be covered. Among the underlying techniques, the RC5 encryption
 algorithm (Appendix B.2.4) is protected by U.S. Patents 5,724,428
 [22] and 5,835,600 [23].
 RC2 and RC5 are trademarks of RSA Security.
 License to copy this document is granted provided that it is
 identified as RSA Security Inc. Public-Key Cryptography Standards
 (PKCS) in all material mentioning or referencing this document.
 RSA Security makes no representations regarding intellectual property
 claims by other parties. Such determination is the responsibility of
 the user.

Revision history

 Versions 1.0-1.3
    Versions 1.0-1.3 were distributed to participants in RSA Data
    Security Inc.'s Public-Key Cryptography Standards meetings in
    February and March 1991.
 Version 1.4
    Version 1.4 was part of the June 3, 1991 initial public release of
    PKCS. Version 1.4 was published as NIST/OSI Implementors' Workshop
    document SEC-SIG-91-20.
 Version 1.5
    Version 1.5 incorporated several editorial changes, including
    updates to the references and the addition of a revision history.
 Version 2.0
    Version 2.0 incorporates major editorial changes in terms of the
    document structure, and introduces the PBES2 encryption scheme,
    the PBMAC1 message authentication scheme, and independent
    password-based key derivation functions. This version continues to
    support the encryption process in version 1.5.

Kaliski Informational [Page 30] RFC 2898 Password-Based Cryptography September 2000

References

 [1]  American National Standard X9.52 - 1998, Triple Data Encryption
      Algorithm Modes of Operation. Working draft, Accredited
      Standards Committee X9, July 27, 1998.
 [2]  Baldwin, R. and R. Rivest, "The RC5, RC5-CBC, RC5-CBC-Pad, and
      RC5-CTS Algorithms", RFC 2040, October 1996.
 [3]  Balenson, D., "Privacy Enhancement for Internet Electronic Mail:
      Part III: Algorithms, Modes, and Identifiers", RFC 1423,
      February 1993.
 [4]  S.M. Bellovin and M. Merritt. Encrypted key exchange:
      Password-based protocols secure against dictionary attacks. In
      Proceedings of the 1992 IEEE Computer Society Conference on
      Research in Security and Privacy, pages 72-84, IEEE Computer
      Society, 1992.
 [5]  D. Jablon. Strong password-only authenticated key exchange. ACM
      Computer Communications Review, October 1996.
 [6]  Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319, April
      1992.
 [7]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
      for Message Authentication", RFC 2104, February 1997.
 [8]  Robert Morris and Ken Thompson. Password security: A case
      history.  Communications of the ACM, 22(11):594-597, November
      1979.
 [9]  ISO/IEC 8824-1:1995: Information technology - Abstract Syntax
      Notation One (ASN.1) - Specification of basic notation. 1995.
 [10] ISO/IEC 8824-1:1995/Amd.1:1995 Information technology - Abstract
      Syntax Notation One (ASN.1) - Specification of basic notation -
      Amendment 1 - Rules of extensibility. 1995.
 [11] ISO/IEC 8824-2:1995 Information technology - Abstract Syntax
      Notation One (ASN.1) - Information object specification. 1995.
 [12] ISO/IEC 8824-2:1995/Amd.1:1995 Information technology - Abstract
      Syntax Notation One (ASN.1) - Information object specification -
      Amendment 1 - Rules of extensibility. 1995.
 [13] ISO/IEC 8824-3:1995 Information technology - Abstract Syntax
      Notation One (ASN.1) - Constraint specification. 1995.

Kaliski Informational [Page 31] RFC 2898 Password-Based Cryptography September 2000

 [14] ISO/IEC 8824-4:1995 Information technology - Abstract Syntax
      Notation One (ASN.1) - Parameterization of ASN.1 specifications.
      1995.
 [15] National Institute of Standards and Technology (NIST). FIPS PUB
      46-2: Data Encryption Standard. December 30, 1993.
 [16] National Institute of Standards and Technology (NIST). FIPS PUB
      81: DES Modes of Operation. December 2, 1980.
 [17] National Institute of Standards and Technology (NIST). FIPS PUB
      112: Password Usage. May 30, 1985.
 [18] National Institute of Standards and Technology (NIST). FIPS PUB
      180-1: Secure Hash Standard. April 1994.
 [19] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April
      1992.
 [20] R.L. Rivest. The RC5 encryption algorithm. In Proceedings of the
      Second International Workshop on Fast Software Encryption, pages
      86-96, Springer-Verlag, 1994.
 [21] Rivest, R., "A Description of the RC2(r) Encryption Algorithm",
      RFC 2268, March 1998.
 [22] R.L. Rivest. Block-Encryption Algorithm with Data-Dependent
      Rotations. U.S. Patent No. 5,724,428, March 3, 1998.
 [23] R.L. Rivest. Block Encryption Algorithm with Data-Dependent
      Rotations. U.S. Patent No. 5,835,600, November 10, 1998.
 [24] RSA Laboratories. PKCS #5: Password-Based Encryption Standard.
      Version 1.5, November 1993.
 [25] RSA Laboratories. PKCS #8: Private-Key Information Syntax
      Standard.  Version 1.2, November 1993.
 [26] T. Wu. The Secure Remote Password protocol. In Proceedings of
      the 1998 Internet Society Network and Distributed System
      Security Symposium, pages 97-111, Internet Society, 1998.
 [27] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
      2279, January 1998.

Kaliski Informational [Page 32] RFC 2898 Password-Based Cryptography September 2000

Contact Information & About PKCS

 The Public-Key Cryptography Standards are specifications produced by
 RSA Laboratories in cooperation with secure systems developers
 worldwide for the purpose of accelerating the deployment of public-
 key cryptography. First published in 1991 as a result of meetings
 with a small group of early adopters of public-key technology, the
 PKCS documents have become widely referenced and implemented.
 Contributions from the PKCS series have become part of many formal
 and de facto standards, including ANSI X9 documents, PKIX, SET,
 S/MIME, and SSL.
 Further development of PKCS occurs through mailing list discussions
 and occasional workshops, and suggestions for improvement are
 welcome. For more information, contact:
      PKCS Editor
      RSA Laboratories
      20 Crosby Drive
      Bedford, MA  01730  USA
      pkcs-editor@rsasecurity.com
      http://www.rsalabs.com/pkcs/

Kaliski Informational [Page 33] RFC 2898 Password-Based Cryptography September 2000

Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Kaliski Informational [Page 34]

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