EVP_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate,
EVP_DigestSignFinal, EVP_DigestSign - EVP signing functions
#include <openssl/evp.h>
int EVP_DigestSignInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
const char *mdname, OSSL_LIB_CTX *libctx,
const char *props, EVP_PKEY *pkey,
const OSSL_PARAM params[]);
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,
size_t tbslen);
The EVP signature routines are a high-level interface to digital signatures.
Input data is digested first before the signing takes place.
EVP_DigestSignInit_ex() sets up signing context
ctx to use a
digest with the name
mdname and private key
pkey. The name of
the digest to be used is passed to the provider of the signature algorithm in
use. How that provider interprets the digest name is provider specific. The
provider may implement that digest directly itself or it may (optionally)
choose to fetch it (which could result in a digest from a different provider
being selected). If the provider supports fetching the digest then it may use
the
props argument for the properties to be used during the fetch.
Finally, the passed parameters
params, if not NULL, are set on the
context before returning.
The
pkey algorithm is used to fetch a
EVP_SIGNATURE method
implicitly, to be used for the actual signing. See "Implicit fetch"
in
provider(7) for more information about implicit fetches.
The OpenSSL default and legacy providers support fetching digests and can fetch
those digests from any available provider. The OpenSSL FIPS provider also
supports fetching digests but will only fetch digests that are themselves
implemented inside the FIPS provider.
ctx must be created with
EVP_MD_CTX_new() before calling this
function. If
pctx 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 is not assigned an EVP_PKEY_CTX value before being passed to
EVP_DigestSignInit_ex() (which means the EVP_PKEY_CTX is created inside
EVP_DigestSignInit_ex() and it will be freed automatically when the
EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by
EVP_DigestSignInit_ex then it will use the
OSSL_LIB_CTX specified in
libctx and the property query string specified in
props.
The digest
mdname may be NULL if the signing algorithm supports it. The
props argument can always be NULL.
No
EVP_PKEY_CTX will be created by
EVP_DigestSignInit_ex() if the
passed
ctx has already been assigned one via
EVP_MD_CTX_set_pkey_ctx(3). See also
SM2(7).
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.
- DSA
- Supports SHA1, SHA224, SHA256, SHA384 and SHA512
- ECDSA
- 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)
- HMAC
- 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.
EVP_DigestSignInit() works in the same way as
EVP_DigestSignInit_ex() except that the
mdname parameter will be
inferred from the supplied digest
type, and
props will be NULL.
Where supplied the ENGINE
e will be used for the signing and digest
algorithm implementations.
e may be NULL.
EVP_DigestSignUpdate() 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.
Unless
sig is NULL
EVP_DigestSignFinal() signs the data in
ctx and places the signature in
sig. Otherwise the maximum
necessary size of the output buffer is written to the
siglen parameter.
If
sig is not NULL 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.
EVP_DigestSign() signs
tbslen bytes of data at
tbs and
places the signature in
sig and its length in
siglen in a
similar way to
EVP_DigestSignFinal(). In the event of a failure
EVP_DigestSign() cannot be called again without reinitialising the
EVP_MD_CTX. If
sig is NULL before the call then
siglen will be
populated with the required size for the
sig buffer. If
sig is
non-NULL before the call then
siglen should contain the length of the
sig buffer.
EVP_DigestSignInit(),
EVP_DigestSignUpdate(),
EVP_DigestSignFinal() and
EVP_DigestSign() return 1 for success
and 0 for failure.
The error codes can be obtained from
ERR_get_error(3).
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.
EVP_DigestSign() 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() and
EVP_DigestSignFinal(). For
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
EVP_dss1() 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. If
the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external
circumstances (see
RAND(7)), the operation will fail.
The call to
EVP_DigestSignFinal() internally finalizes a copy of the
digest context. This means that calls to
EVP_DigestSignUpdate() and
EVP_DigestSignFinal() can be called later to digest and sign additional
data.
EVP_DigestSignInit() and
EVP_DigestSignInit_ex() functions can be
called multiple times on a context and the parameters set by previous calls
should be preserved if the
pkey parameter is NULL. The call then just
resets the state of the
ctx.
Ignoring failure returns of
EVP_DigestSignInit() and
EVP_DigestSignInit_ex() functions can lead to subsequent undefined
behavior when calling
EVP_DigestSignUpdate(),
EVP_DigestSignFinal(), or
EVP_DigestSign().
The use of
EVP_PKEY_get_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_get_size() would have to
return a value which indicates the maximum possible signature for any set of
parameters.
EVP_DigestVerifyInit(3),
EVP_DigestInit(3),
evp(7),
HMAC(3),
MD2(3),
MD5(3),
MDC2(3),
RIPEMD160(3),
SHA1(3),
openssl-dgst(1),
RAND(7)
EVP_DigestSignInit(),
EVP_DigestSignUpdate() and
EVP_DigestSignFinal() were added in OpenSSL 1.0.0.
EVP_DigestSignInit_ex() was added in OpenSSL 3.0.
EVP_DigestSignUpdate() was converted from a macro to a function in
OpenSSL 3.0.
Copyright 2006-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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
<
https://www.openssl.org/source/license.html>.