EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing
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, size_t cnt);
int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
The EVP signature routines are a high level interface to digital signatures.
sets up signing context ctx
to use digest
from ENGINE impl
and private key pkey
must be created with EVP_MD_CTX_new()
before calling this function. If
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.
bytes of data at d
the signature context ctx
. This function can be called several times on
the same ctx
to include additional data. This function is currently
implemented using a macro.
signs the data in ctx
places the signature
. If sig
then the maximum size of the
output buffer is written to the siglen
parameter. If sig
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 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)
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
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()
can be called later to digest and sign additional
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
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
were first added to OpenSSL 1.0.0.
Copyright 2006-2017 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at