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. 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.
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.
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.