EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal, EVP_DigestSign -
EVP signing functions
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);
int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
size_t *siglen, const unsigned char *tbs,
The EVP signature routines are a high level interface to digital signatures.
sets up signing context ctx
to use digest
from ENGINE e
and private key pkey
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.
Note that any existing value in *pctx
is overwritten. The EVP_PKEY_CTX
value returned must not be freed directly by the application if ctx
not assigned an EVP_PKEY_CTX value before being passed to
(which means the EVP_PKEY_CTX is created inside
and it will be freed automatically when the
EVP_MD_CTX is freed).
The digest type
may be NULL if the signing algorithm supports it.
will be created by EVP_DigsetSignInit()
has already been assigned one via
(3). See also SM2
Only EVP_PKEY types that support signing can be used with these functions. This
includes MAC algorithms where the MAC generation is considered as a form of
"signing". Built-in EVP_PKEY types supported by these functions are
CMAC, Poly1305, DSA, ECDSA, HMAC, RSA, SipHash, Ed25519 and Ed448.
Not all digests can be used for all key types. The following combinations apply.
- Supports SHA1, SHA224, SHA256, SHA384 and SHA512
- Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
- RSA with no padding
- Supports no digests (the digest type must be NULL)
- RSA with X931 padding
- Supports SHA1, SHA256, SHA384 and SHA512
- All other RSA padding types
- Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4,
MDC2, SHA3-224, SHA3-256, SHA3-384, SHA3-512
- Ed25519 and Ed448
- Support no digests (the digest type must be NULL)
- Supports any digest
- CMAC, Poly1305 and SipHash
- Will ignore any digest provided.
If RSA-PSS is used and restrictions apply then the digest must match.
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
and places the
signature in sig
. If sig
then the maximum size of
the output buffer is written to the siglen
parameter. If sig
then before the call the siglen
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
bytes of data at tbs
places the signature in sig
and its length in siglen
similar way to EVP_DigestSignFinal()
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
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.
is a one shot operation which signs a single block of
data in one function. For algorithms that support streaming it is equivalent
to calling EVP_DigestSignUpdate()
algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
to sign data.
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_free()
or a memory leak will
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 2006-2018 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