EVP_PKEY_size, EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal -
EVP signing functions
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);
The EVP signature routines are a high level interface to digital signatures.
sets up signing context ctx
to use digest
from ENGINE impl
must be created with
before calling this function.
bytes of data at d
signature context ctx
. This function can be called several times on the
to include additional data.
signs the data in ctx
using the private key
and places the signature in sig
must be at
least EVP_PKEY_size(pkey) bytes in size. s
is an OUT parameter, and not
used as an IN parameter. 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.
initializes a signing context ctx
to use the
default implementation of digest type
returns the maximum size of a signature in bytes. The
actual signature returned by EVP_SignFinal()
may be smaller.
return 1 for success and 0 for failure.
returns the maximum size of a signature in bytes.
The error codes can be obtained by 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.
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
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()
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
Older versions of this documentation wrongly stated that calls to
could not be made after calling
Since the private key is passed in the call to EVP_SignFinal()
relating to the private key (for example an unsuitable key and digest
combination) will not be indicated until after potentially large amounts of
data have been passed through EVP_SignUpdate()
It is not possible to change the signing parameters using these function.
The previous two bugs are fixed in the newer EVP_SignDigest*() function.
Copyright 2000-2017 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