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NAME

     EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing
     functions



SYNOPSIS
      #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
     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
     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
     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
     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
     EVP_VerifyInit(3), EVP_DigestInit(3), err(3), evp(3),
     hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3),
     digest(1)



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









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Created 1996-2024 by Maxim Chirkov

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