OpenSSL 1.1.1-pre2
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Hakase
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=pod
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=head1 NAME
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EVP_PKEY_size,
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EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal,
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EVP_PKEY_security_bits - EVP signing
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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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int EVP_PKEY_size(EVP_PKEY *pkey);
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int EVP_PKEY_security_bits(const EVP_PKEY *pkey);
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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 B<ctx> to use digest
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B<type> from ENGINE B<impl>. B<ctx> must be created with
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EVP_MD_CTX_new() before calling this function.
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EVP_SignUpdate() 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.
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EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and
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places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey)
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bytes in size. B<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 B<s>, at most EVP_PKEY_size(pkey) bytes
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will be written.
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EVP_SignInit() initializes a signing context B<ctx> to use the default
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implementation of digest B<type>.
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EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
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signature returned by EVP_SignFinal() may be smaller.
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EVP_PKEY_security_bits() returns the number of security bits of the given B<pkey>,
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bits of security is defined in NIST SP800-57.
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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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EVP_PKEY_size() returns the maximum size of a signature in bytes.
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The error codes can be obtained by L<ERR_get_error(3)>.
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EVP_PKEY_security_bits() returns the number of security bits.
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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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Due to the link between message digests and public key algorithms the correct
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digest algorithm must be used with the correct public key type. A list of
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algorithms and associated public key algorithms appears in
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L<EVP_DigestInit(3)>.
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When signing with DSA private keys the random number generator must be seeded
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or the operation will fail. The random number generator does not need to be
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seeded 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_cleanup() 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_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 2000-2017 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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