NAME
EVP_SignInit_ex,
EVP_SignUpdate,
EVP_SignFinal, EVP_SignInit,
EVP_PKEY_size —
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 a signing context ctx to use the digest
type from ENGINE
impl. ctx must be initialized
with
EVP_MD_CTX_init(3) 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. 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.
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.
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).
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(3) or a memory leak will occur.
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).
SEE ALSO
ERR(3), evp(3), EVP_DigestInit(3), EVP_PKEY_asn1_set_public(3), EVP_VerifyInit(3)
HISTORY
EVP_SignInit(),
EVP_SignUpdate(),
EVP_SignFinal(), and
EVP_PKEY_size() appeared in SSLeay 0.8.1b or earlier
and have been available since OpenBSD 2.4.
EVP_SignInit_ex() first appeared in
OpenSSL 0.9.7 and has been available since OpenBSD
3.2.
BUGS
Older versions of this documentation wrongly stated that calls to
EVP_SignUpdate() could not be made after calling
EVP_SignFinal().
Since the private key is passed in the call to
EVP_SignFinal() any error 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.