X931Signer (Bouncy Castle Library 1.85 API Specification)
Date: 2026-07-12

org.bouncycastle.crypto.signers

## Class X931Signer

- java.lang.Object
- - org.bouncycastle.crypto.signers.X931Signer

- All Implemented Interfaces:
    Signer

      public class X931Signer
      extends java.lang.Object
      implements Signer

  X9.31-1998 - signing using a hash.

  The message digest hash, H, is encapsulated to form a byte string as follows

       EB = 06 || PS || 0xBA || H || TRAILER

  where PS is a string of bytes all of value 0xBB of length such that |EB|=|n|, and TRAILER is the ISO/IEC 10118 part number† for the digest. The byte string, EB, is converted to an integer value, the message representative, f.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `TRAILER_IMPLICIT` Deprecated. use ISOTrailers
    `static int` | `TRAILER_RIPEMD128` Deprecated. use ISOTrailers
    `static int` | `TRAILER_RIPEMD160` Deprecated. use ISOTrailers
    `static int` | `TRAILER_SHA1` Deprecated. use ISOTrailers
    `static int` | `TRAILER_SHA224` Deprecated. use ISOTrailers
    `static int` | `TRAILER_SHA256` Deprecated. use ISOTrailers
    `static int` | `TRAILER_SHA384` Deprecated. use ISOTrailers
    `static int` | `TRAILER_SHA512` Deprecated. use ISOTrailers
    `static int` | `TRAILER_WHIRLPOOL` Deprecated. use ISOTrailers

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `X931Signer(AsymmetricBlockCipher cipher, Digest digest)` Constructor for a signer with an explicit digest trailer.
    `X931Signer(AsymmetricBlockCipher cipher, Digest digest, boolean implicit)` Generate a signer with either implicit or explicit trailers for X9.31

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `byte[]` | `generateSignature()` generate a signature for the loaded message using the key we were initialised with.
    `void` | `init(boolean forSigning, CipherParameters param)` Initialise the signer for signing or verification.
    `void` | `reset()` reset the internal state
    `void` | `update(byte b)` update the internal digest with the byte b
    `void` | `update(byte[] in, int off, int len)` update the internal digest with the byte array in
    `boolean` | `verifySignature(byte[] signature)` return true if the signature represents a X9.31 signature for the passed in message.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### TRAILER_IMPLICIT

          public static final int TRAILER_IMPLICIT

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_RIPEMD160

          public static final int TRAILER_RIPEMD160

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_RIPEMD128

          public static final int TRAILER_RIPEMD128

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_SHA1

          public static final int TRAILER_SHA1

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_SHA256

          public static final int TRAILER_SHA256

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_SHA512

          public static final int TRAILER_SHA512

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_SHA384

          public static final int TRAILER_SHA384

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_WHIRLPOOL

          public static final int TRAILER_WHIRLPOOL

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

    - #### TRAILER_SHA224

          public static final int TRAILER_SHA224

      Deprecated. use ISOTrailers
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### X931Signer

          public X931Signer(AsymmetricBlockCipher cipher,
                            Digest digest,
                            boolean implicit)

      Generate a signer with either implicit or explicit trailers for X9.31
      Parameters:
        `cipher` - base cipher to use for signature creation/verification
        `digest` - digest to use.
        `implicit` - whether or not the trailer is implicit or gives the hash.

    - #### X931Signer

          public X931Signer(AsymmetricBlockCipher cipher,
                            Digest digest)

      Constructor for a signer with an explicit digest trailer.
      Parameters:
        `cipher` - cipher to use.
        `digest` - digest to sign with.

  - ### Method Detail

    - #### init

          public void init(boolean forSigning,
                           CipherParameters param)

      Description copied from interface: `Signer`
      Initialise the signer for signing or verification.
      Specified by:
        `init` in interface `Signer`
      Parameters:
        `forSigning` - true if for signing, false otherwise
        `param` - necessary parameters.

    - #### update

          public void update(byte b)

      update the internal digest with the byte b
      Specified by:
        `update` in interface `Signer`

    - #### update

          public void update(byte[] in,
                             int off,
                             int len)

      update the internal digest with the byte array in
      Specified by:
        `update` in interface `Signer`

    - #### reset

          public void reset()

      reset the internal state
      Specified by:
        `reset` in interface `Signer`

    - #### generateSignature

          public byte[] generateSignature()
                                   throws CryptoException

      generate a signature for the loaded message using the key we were initialised with.
      Specified by:
        `generateSignature` in interface `Signer`
      Throws:
        `CryptoException`

    - #### verifySignature

          public boolean verifySignature(byte[] signature)

      return true if the signature represents a X9.31 signature for the passed in message.
      Specified by:
        `verifySignature` in interface `Signer`