NAME¶
EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing
functions
SYNOPSIS¶
#include <openssl/evp.h>
int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
DESCRIPTION¶
The EVP signature routines are a high level interface to digital signatures.
EVP_DigestSignInit() sets up signing context
ctx to use digest
type from ENGINE
impl and private key
pkey.
ctx
must be initialized with
EVP_MD_CTX_init() before calling this
function. If
pctx is not NULL the EVP_PKEY_CTX of the signing operation
will be written to
*pctx: this can be used to set alternative signing
options.
EVP_DigestSignUpdate() 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. This function is currently
implemented usig a macro.
EVP_DigestSignFinal() signs the data in
ctx places the signature
in
sig. If
sig is
NULL then the maximum size of the
output buffer is written to the
siglen parameter. If
sig is not
NULL then before the call the
siglen parameter should contain
the length of the
sig buffer, if the call is successful the signature
is written to
sig and the amount of data written to
siglen.
RETURN VALUES¶
EVP_DigestSignInit() EVP_DigestSignUpdate() and
EVP_DigestSignaFinal() return 1 for success and 0 or a negative value
for failure. In particular a return value of -2 indicates the operation is not
supported by the public key algorithm.
The error codes can be obtained from
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.
In previous versions of OpenSSL there was a link between message digest types
and public key algorithms. This meant that "clone" digests such as
EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
longer necessary and the use of clone digest is now discouraged.
For some key types and parameters the random number generator must be seeded or
the operation will fail.
The call to
EVP_DigestSignFinal() internally finalizes a copy of the
digest context. This means that calls to
EVP_DigestSignUpdate() and
EVP_DigestSignFinal() 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.
The use of
EVP_PKEY_size() with these functions is discouraged because
some signature operations may have a signature length which depends on the
parameters set. As a result
EVP_PKEY_size() would have to return a
value which indicates the maximum possible signature for any set of
parameters.
SEE ALSO¶
EVP_DigestVerifyInit(3),
EVP_DigestInit(3),
err(3),
evp(3),
hmac(3),
md2(3),
md5(3),
mdc2(3),
ripemd(3),
sha(3),
dgst(1)
HISTORY¶
EVP_DigestSignInit(),
EVP_DigestSignUpdate() and
EVP_DigestSignFinal() were first added to OpenSSL 1.0.0.