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EVP_DigestSignInit(3)               OpenSSL              EVP_DigestSignInit(3)



NAME
       EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP
       signing functions

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                               const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
        int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
        int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);

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

       EVP_DigestSignInit() sets up signing context ctx to use digest type
       from ENGINE impl and private key pkey. ctx must be initialized with
       EVP_MD_CTX_init() before calling this function. If pctx is not NULL the
       EVP_PKEY_CTX of the signing operation will be written to *pctx: this
       can be used to set alternative signing options.

       EVP_DigestSignUpdate() 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. This function is currently implemented usig
       a macro.

       EVP_DigestSignFinal() signs the data in ctx places the signature in
       sig.  If sig is NULL then the maximum size of the output buffer is
       written to the siglen parameter. If sig is not NULL then before the
       call the siglen parameter should contain the length of the sig buffer,
       if the call is successful the signature is written to sig and the
       amount of data written to siglen.

RETURN VALUES
       EVP_DigestSignInit() EVP_DigestSignUpdate() and EVP_DigestSignaFinal()
       return 1 for success and 0 or a negative value for failure. In
       particular a return value of -2 indicates the operation is not
       supported by the public key algorithm.

       The error codes can be obtained from 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 used and much more flexible.

       In previous versions of OpenSSL there was a link between message digest
       types and public key algorithms. This meant that "clone" digests such
       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
       longer necessary and the use of clone digest is now discouraged.

       For some key types and parameters the random number generator must be
       seeded or the operation will fail.

       The call to EVP_DigestSignFinal() internally finalizes a copy of the
       digest context. This means that calls to EVP_DigestSignUpdate() and
       EVP_DigestSignFinal() 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.

       The use of EVP_PKEY_size() with these functions is discouraged because
       some signature operations may have a signature length which depends on
       the parameters set. As a result EVP_PKEY_size() would have to return a
       value which indicates the maximum possible signature for any set of
       parameters.

SEE ALSO
       EVP_DigestVerifyInit(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
       EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
       were first added to OpenSSL 1.0.0.



1.0.2k                            2017-01-27             EVP_DigestSignInit(3)