NAME    [Toc]    [Back]

       EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing
       functions

SYNOPSIS    [Toc]    [Back]

        #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    [Toc]    [Back]

       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 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.

       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_SignFinal()
       may be smaller.

RETURN VALUES    [Toc]    [Back]

       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    [Toc]    [Back]

       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 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_SignUp-
       date() and EVP_SignFinal() can be called later to digest
       and sign additional data.

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

BUGS    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

       EVP_VerifyInit(3), EVP_DigestInit(3), ERR_get_error(3),
       evp(3), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD(3),
       SHA1(3), digest(1)

HISTORY    [Toc]    [Back]

       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.


OpenBSD 3.6                 2002-09-10                          2