NAME    [Toc]    [Back]

       EVP_SignInit,  EVP_SignUpdate, EVP_SignFinal - EVP signing
       functions

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.

       The EVP_SignInit() function initializes a signing  context
       ctx to using digest type. This typically will  be supplied
       by a function such as EVP_sha1().

       The EVP_SignUpdate() function 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.

       The  EVP_SignFinal()  function 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 the
       EVP_SignInit() function can be called to initialize a  new
       signature operation.

       The EVP_PKEY_size() function returns the maximum size of a
       signature in bytes. The actual signature returned  by  the
       EVP_SignFinal() function may be smaller.

NOTES    [Toc]    [Back]

       The  EVP interface to digital signatures should 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.

RESTRICTIONS    [Toc]    [Back]

       Several  of  the  functions do not return values. Although
       the internal digest operations will never fail some future
       hardware based operations might.

RETURN VALUES    [Toc]    [Back]

       The  EVP_SignInit()  and EVP_SignUpdate() functions do not
       return values.

       The EVP_SignFinal() function returns 1 for success  and  0
       for failure.

       The EVP_PKEY_size() function returns the maximum size of a
       signature in bytes.

       The error codes can be obtained by using  ERR_get_error().

HISTORY    [Toc]    [Back]

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

SEE ALSO    [Toc]    [Back]

       Commands: dgst(1)

       Functions:  EVP_VerifyInit(3),  EVP_DigestInit(3), err(3),
       evp(3),  hmac(3),  md2(3),  md5(3),  mdc2(3),   ripemd(3),
       sha(3),



                                                  EVP_SignInit(3)