NAME    [Toc]    [Back]

       EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing
       functions

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #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    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [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.

BUGS    [Toc]    [Back]

       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    [Toc]    [Back]

       EVP_VerifyInit(3), EVP_DigestInit(3), openssl_err(3),
       openssl_evp(3), openssl_hmac(3), md2(3), openssl_md5(3),
       openssl_mdc2(3), openssl_ripemd(3), openssl_sha(3),
       openssl_dgst(1)

HISTORY    [Toc]    [Back]

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



2002-07-31                    0.9.6g              EVP_SignInit(3)