EVP_SignInit(3)             OpenSSL             EVP_SignInit(3)





NAME
       EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP sign-
       ing functions

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
        int 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);

        void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);

        int EVP_PKEY_size(EVP_PKEY *pkey);

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

       EVP_SignInit_ex() sets up signing context ctx to use
       digest type from ENGINE impl. ctx must be initialized
       with EVP_MD_CTX_init() before calling this function.

       EVP_SignUpdate() hashes cnt bytes of data at d into the
       signature context ctx. This function can be called sev-
       eral 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 writ-
       ten to the integer at s, at most EVP_PKEY_size(pkey)
       bytes will be written.

       EVP_SignInit() initializes a signing context ctx to use
       the default implementation of digest type.

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

RETURN VALUES
       EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal()
       return 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 inter-
       faces. This is because the code then becomes transparent
       to the algorithm 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.

       The call to EVP_SignFinal() internally finalizes a copy
       of the digest context.  This means that calls to
       EVP_SignUpdate() and EVP_SignFinal() can be called later
       to digest and sign additional data.

       Since only a copy of the digest context is ever final-
       ized the context must be cleaned up after use by calling
       EVP_MD_CTX_cleanup() or a memory leak will occur.

BUGS
       Older versions of this documentation wrongly stated that
       calls to EVP_SignUpdate() could not be made after call-
       ing EVP_SignFinal().

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.

       EVP_SignInit_ex() was added in OpenSSL 0.9.7.



0.9.7c                     2002-07-18           EVP_SignInit(3)
