/usr/man/cat.3/EVP_SignFinal.3

EVP_SignInit(3)              OpenSSL              EVP_SignInit(3)

NAME

     EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal
     - EVP signing 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 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. sig must be at least
     EVP_PKEY_size(pkey) bytes in size. s is an OUT paramter, and
     not used as an IN parameter.  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

     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).

1.0.2t               Last change: 2019-09-10                    1

EVP_SignInit(3)              OpenSSL              EVP_SignInit(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.

     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 finalized
     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 calling
     EVP_SignFinal().

     Since the private key is passed in the call to
     EVP_SignFinal() any error relating to the private key (for
     example an unsuitable key and digest combination) will not
     be indicated until after potentially large amounts of data
     have been passed through EVP_SignUpdate().

     It is not possible to change the signing parameters using
     these function.

     The previous two bugs are fixed in the newer
     EVP_SignDigest*() function.

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.

1.0.2t               Last change: 2019-09-10                    2

EVP_SignInit(3)              OpenSSL              EVP_SignInit(3)

     EVP_SignInit_ex() was added in OpenSSL 0.9.7.

1.0.2t               Last change: 2019-09-10                    3

See also EVP_SignInit(3)
See also EVP_SignInit_ex(3)
See also EVP_SignUpdate(3)