NAME
EVP_SignInit, 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. 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.
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).
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.
Restrictions
Older versions of this documentation wrongly stated that calls
to EVP_SignUpdate() could not be made after calling EVP_SignFinal().
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.
EVP_SignInit_ex() was added in OpenSSL 0.9.7.