100 lines
3.5 KiB
Plaintext
100 lines
3.5 KiB
Plaintext
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=pod
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=head1 NAME
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EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal
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- EVP signing functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);
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void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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=head1 DESCRIPTION
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The EVP signature routines are a high-level interface to digital
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signatures.
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EVP_SignInit_ex() sets up signing context I<ctx> to use digest
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I<type> from B<ENGINE> I<impl>. I<ctx> must be created with
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EVP_MD_CTX_new() before calling this function.
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EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the
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signature context I<ctx>. This function can be called several times on the
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same I<ctx> to include additional data.
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EVP_SignFinal() signs the data in I<ctx> using the private key I<pkey> and
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places the signature in I<sig>. I<sig> must be at least C<EVP_PKEY_size(pkey)>
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bytes in size. I<s> is an OUT parameter, and not used as an IN parameter.
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The number of bytes of data written (i.e. the length of the signature)
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will be written to the integer at I<s>, at most C<EVP_PKEY_size(pkey)> bytes
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will be written.
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EVP_SignInit() initializes a signing context I<ctx> to use the default
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implementation of digest I<type>.
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=head1 RETURN VALUES
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EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
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for success and 0 for failure.
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The error codes can be obtained by 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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When signing with DSA private keys 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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This requirement does not hold for RSA signatures.
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The call to EVP_SignFinal() internally finalizes a copy of the digest context.
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This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
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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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=head1 BUGS
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Older versions of this documentation wrongly stated that calls to
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EVP_SignUpdate() could not be made after calling EVP_SignFinal().
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Since the private key is passed in the call to EVP_SignFinal() any error
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relating to the private key (for example an unsuitable key and digest
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combination) will not be indicated until after potentially large amounts of
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data have been passed through EVP_SignUpdate().
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It is not possible to change the signing parameters using these function.
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The previous two bugs are fixed in the newer EVP_SignDigest*() function.
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=head1 SEE ALSO
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L<EVP_PKEY_size(3)>, L<EVP_PKEY_bits(3)>, L<EVP_PKEY_security_bits(3)>,
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L<EVP_VerifyInit(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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=head1 COPYRIGHT
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Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (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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