EMSA_PSS (GNU cryptographic primitives and tools)
Keywords: gnu.crypto.sig.rsa.EMSA_PSS,EMSA_PSS class

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## gnu.crypto.sig.rsa
Class EMSA_PSS

    java.lang.Object
      |
      +--gnu.crypto.sig.rsa.EMSA_PSS

All Implemented Interfaces:
  java.lang.Cloneable

public class EMSA_PSS
extends java.lang.Object
implements java.lang.Cloneable

An implementation of the EMSA-PSS encoding/decoding scheme.

EMSA-PSS coincides with EMSA4 in IEEE P1363a D5 except that EMSA-PSS acts on octet strings and not on bit strings. In particular, the bit lengths of the hash and the salt must be multiples of 8 in EMSA-PSS. Moreover, EMSA4 outputs an integer of a desired bit length rather than an octet string.

EMSA-PSS is parameterized by the choice of hash function Hash and mask generation function MGF. In this submission, MGF is based on a Hash definition that coincides with the corresponding definitions in IEEE Std 1363-2000, PKCS #1 v2.0, and the draft ANSI X9.44. In PKCS #1 v2.0 and the draft ANSI X9.44, the recommended hash function is SHA-1, while IEEE Std 1363-2000 recommends SHA-1 and RIPEMD-160.

References:

1. RSA-PSS Signature Scheme with Appendix, part B.
   Primitive specification and supporting documentation.
   Jakob Jonsson and Burt Kaliski.

Method Summary
`java.lang.Object` | `clone()`
`boolean` | `decode(byte[] mHash, byte[] EM, int emBits, int sLen)` The decoding operation EMSA-PSS-Decode recovers the message hash from an encoded message `EM` and compares it to the hash of `M`.
`byte[]` | `encode(byte[] mHash, int emBits, byte[] salt)` The encoding operation EMSA-PSS-Encode computes the hash of a message `M` using a hash function and maps the result to an encoded message `EM` of a specified length using a mask generation function.
`static EMSA_PSS` | `getInstance(java.lang.String mdName)` Returns an instance of this object given a designated name of a hash function.

Methods inherited from class java.lang.Object
`equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Method Detail

### getInstance

    public static EMSA_PSS getInstance(java.lang.String mdName)

  Returns an instance of this object given a designated name of a hash function.

  Parameters:
    `mdName` - the canonical name of a hash function.
  Returns:
    an instance of this object configured for use with the designated options.

### clone

    public java.lang.Object clone()

  Overrides:
    `clone` in class `java.lang.Object`

### encode

    public byte[] encode(byte[] mHash,
                         int emBits,
                         byte[] salt)

  The encoding operation EMSA-PSS-Encode computes the hash of a message `M` using a hash function and maps the result to an encoded message `EM` of a specified length using a mask generation function.

  Parameters:
    `mHash` - the byte sequence resulting from applying the message digest algorithm Hash to the message M.
    `emBits` - the maximal bit length of the integer OS2IP(EM), at least `8.hLen + 8.sLen + 9`.
    `salt` - the salt to use when encoding the output.
  Returns:
    the encoded message `EM`, an octet string of length `emLen = CEILING(emBits / 8)`.
  Throws:
    `java.lang.IllegalArgumentException` - if an exception occurs.

### decode

    public boolean decode(byte[] mHash,
                          byte[] EM,
                          int emBits,
                          int sLen)

  The decoding operation EMSA-PSS-Decode recovers the message hash from an encoded message `EM` and compares it to the hash of `M`.

  Parameters:
    `mHash` - the byte sequence resulting from applying the message digest algorithm Hash to the message M.
    `EM` - the encoded message, an octet string of length `emLen = CEILING(emBits/8).`
    `emBits` - the maximal bit length of the integer OS2IP(EM), at least `8.hLen + 8.sLen + 9`.
    `sLen` - the length, in octets, of the expected salt.
  Returns:
    `true` if the result of the verification was consistent with the expected reseult; and `false` if the result was inconsistent.
  Throws:
    `java.lang.IllegalArgumentException` - if an exception occurs.

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Copyright © 2001, 2002, 2003, 2004 Free Software Foundation, Inc.