EVP_SignInit(3) OpenSSL EVP_SignInit(3)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 VALUESEVP_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
26/Feb/2001 0.9.6 1
EVP_SignInit(3) OpenSSL EVP_SignInit(3)
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 ALSOEVP_VerifyInit(3), EVP_DigestInit(3), err(3), evp(3),
hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3),
digest(1)HISTORYEVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
available in all versions of SSLeay and OpenSSL.
26/Feb/2001 0.9.6 2