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The manual pages require for some API functions that the 'random number generator must be seeded' before calling the function. Initially, this was meant literally, i.e. the OpenSSL CSPRNG had to be seeded manually before calling these functions. Since version 1.1.1, the CSPRNG is seeded automatically on first use, so it's not the responsibility of the programmer anymore. Still, he needs to be aware that the seeding might fail. Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org> (Merged from https://github.com/openssl/openssl/pull/9257)
169 lines
6.1 KiB
Plaintext
169 lines
6.1 KiB
Plaintext
=pod
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=head1 NAME
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EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal,
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EVP_DigestSign - EVP signing functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
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int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
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size_t *siglen, const unsigned char *tbs,
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size_t tbslen);
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=head1 DESCRIPTION
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The EVP signature routines are a high level interface to digital signatures.
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EVP_DigestSignInit() sets up signing context B<ctx> to use digest B<type> from
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ENGINE B<e> and private key B<pkey>. B<ctx> must be created with
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EVP_MD_CTX_new() before calling this function. If B<pctx> is not NULL, the
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EVP_PKEY_CTX of the signing operation will be written to B<*pctx>: this can
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be used to set alternative signing options. Note that any existing value in
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B<*pctx> is overwritten. The EVP_PKEY_CTX value returned must not be freed
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directly by the application if B<ctx> is not assigned an EVP_PKEY_CTX value before
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being passed to EVP_DigestSignInit() (which means the EVP_PKEY_CTX is created
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inside EVP_DigestSignInit() and it will be freed automatically when the
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EVP_MD_CTX is freed).
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The digest B<type> may be NULL if the signing algorithm supports it.
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No B<EVP_PKEY_CTX> will be created by EVP_DigsetSignInit() if the passed B<ctx>
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has already been assigned one via L<EVP_MD_CTX_set_ctx(3)>. See also L<SM2(7)>.
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Only EVP_PKEY types that support signing can be used with these functions. This
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includes MAC algorithms where the MAC generation is considered as a form of
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"signing". Built-in EVP_PKEY types supported by these functions are CMAC,
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Poly1305, DSA, ECDSA, HMAC, RSA, SipHash, Ed25519 and Ed448.
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Not all digests can be used for all key types. The following combinations apply.
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=over 4
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=item DSA
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Supports SHA1, SHA224, SHA256, SHA384 and SHA512
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=item ECDSA
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Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
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=item RSA with no padding
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Supports no digests (the digest B<type> must be NULL)
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=item RSA with X931 padding
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Supports SHA1, SHA256, SHA384 and SHA512
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=item All other RSA padding types
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Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4, MDC2,
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SHA3-224, SHA3-256, SHA3-384, SHA3-512
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=item Ed25519 and Ed448
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Support no digests (the digest B<type> must be NULL)
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=item HMAC
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Supports any digest
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=item CMAC, Poly1305 and SipHash
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Will ignore any digest provided.
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=back
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If RSA-PSS is used and restrictions apply then the digest must match.
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EVP_DigestSignUpdate() hashes B<cnt> bytes of data at B<d> into the
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signature context B<ctx>. This function can be called several times on the
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same B<ctx> to include additional data. This function is currently implemented
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using a macro.
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EVP_DigestSignFinal() signs the data in B<ctx> and places the signature in B<sig>.
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If B<sig> is B<NULL> then the maximum size of the output buffer is written to
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the B<siglen> parameter. If B<sig> is not B<NULL> then before the call the
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B<siglen> parameter should contain the length of the B<sig> buffer. If the
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call is successful the signature is written to B<sig> and the amount of data
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written to B<siglen>.
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EVP_DigestSign() signs B<tbslen> bytes of data at B<tbs> and places the
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signature in B<sig> and its length in B<siglen> in a similar way to
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EVP_DigestSignFinal().
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=head1 RETURN VALUES
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EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignaFinal() and
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EVP_DigestSign() return 1 for success and 0 or a negative value for failure. In
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particular, a return value of -2 indicates the operation is not supported by the
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public key algorithm.
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The error codes can be obtained from L<ERR_get_error(3)>.
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=head1 NOTES
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The B<EVP> interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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EVP_DigestSign() is a one shot operation which signs a single block of data
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in one function. For algorithms that support streaming it is equivalent to
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calling EVP_DigestSignUpdate() and EVP_DigestSignFinal(). For algorithms which
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do not support streaming (e.g. PureEdDSA) it is the only way to sign data.
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.
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For some key types and parameters the random number generator must be seeded.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see L<RAND(7)>), the operation will fail.
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The call to EVP_DigestSignFinal() internally finalizes a copy of the digest
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context. This means that calls to EVP_DigestSignUpdate() and
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EVP_DigestSignFinal() can be called later to digest and sign additional data.
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Since only a copy of the digest context is ever finalized, the context must
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be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
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will occur.
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The use of EVP_PKEY_size() with these functions is discouraged because some
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signature operations may have a signature length which depends on the
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parameters set. As a result EVP_PKEY_size() would have to return a value
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which indicates the maximum possible signature for any set of parameters.
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=head1 SEE ALSO
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L<EVP_DigestVerifyInit(3)>,
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L<EVP_DigestInit(3)>,
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L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
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L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
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L<SHA1(3)>, L<dgst(1)>,
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L<RAND(7)>
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=head1 HISTORY
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EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
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were added in OpenSSL 1.0.0.
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=head1 COPYRIGHT
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Copyright 2006-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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