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EVP_DIGESTSIGNINIT(3ossl) OpenSSL EVP_DIGESTSIGNINIT(3ossl)
NAME
EVP_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate,
EVP_DigestSignFinal, EVP_DigestSign - EVP signing functions
SYNOPSIS
#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);
DESCRIPTION
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.
RETURN VALUES
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).
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.
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.
SEE ALSO
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)
HISTORY
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
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>.
3.0.14 2024-06-04 EVP_DIGESTSIGNINIT(3ossl)
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