EVP_SignInit(3)

     EVP_SignInit(3)        0.9.6h (2002-07-10)        EVP_SignInit(3)

     NAME
          EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing
          functions

     SYNOPSIS
           #include <openssl/evp.h>

           void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
           void EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
           int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);

           int EVP_PKEY_size(EVP_PKEY *pkey);

     DESCRIPTION
          The EVP signature routines are a high level interface to
          digital signatures.

          EVP_SignInit() initializes a signing context ctx to using
          digest type: this will typically be supplied by a function
          such as EVP_sha1().

          EVP_SignUpdate() hashes cnt bytes of data at d into the
          signature context ctx. This function can be called several
          times on the same ctx to include additional data.

          EVP_SignFinal() signs the data in ctx using the private key
          pkey and places the signature in sig. If the s parameter is
          not NULL then the number of bytes of data written (i.e. the
          length of the signature) will be written to the integer at
          s, at most EVP_PKEY_size(pkey) bytes will be written.  After
          calling EVP_SignFinal() no additional calls to
          EVP_SignUpdate() can be made, but EVP_SignInit() can be
          called to initialize a new signature operation.

          EVP_PKEY_size() returns the maximum size of a signature in
          bytes. The actual signature returned by EVP_SignFinal() may
          be smaller.

     RETURN VALUES
          EVP_SignInit() and EVP_SignUpdate() do not return values.

          EVP_SignFinal() returns 1 for success and 0 for failure.

          EVP_PKEY_size() returns the maximum size of a signature in
          bytes.

          The error codes can be obtained by ERR_get_error(3).

     NOTES
          The EVP interface to digital signatures should almost always
          be used in preference to the low level interfaces. This is
          because the code then becomes transparent to the algorithm

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     EVP_SignInit(3)        0.9.6h (2002-07-10)        EVP_SignInit(3)

          used and much more flexible.

          Due to the link between message digests and public key
          algorithms the correct digest algorithm must be used with
          the correct public key type. A list of algorithms and
          associated public key algorithms appears in
          EVP_DigestInit(3).

          When signing with DSA private keys the random number
          generator must be seeded or the operation will fail. The
          random number generator does not need to be seeded for RSA
          signatures.

     BUGS
          Several of the functions do not return values: maybe they
          should. Although the internal digest operations will never
          fail some future hardware based operations might.

     SEE ALSO
          EVP_VerifyInit(3), EVP_DigestInit(3), err(3), evp(3),
          hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)

     HISTORY
          EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
          available in all versions of SSLeay and OpenSSL.

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