140 lines
4.7 KiB
Plaintext
140 lines
4.7 KiB
Plaintext
=pod
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=head1 NAME
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EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - 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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=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<impl> 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 (it will be freed automatically when the EVP_MD_CTX
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is freed). The digest B<type> may be NULL if the signing algorithm supports it.
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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, DSA,
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ECDSA, HMAC and RSA.
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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 and SHA512
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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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RIPEMD160
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=item HMAC
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Supports any digest
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=item CMAC
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Will ignore any digest provided.
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=back
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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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=head1 RETURN VALUES
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EVP_DigestSignInit() EVP_DigestSignUpdate() and EVP_DigestSignaFinal() return
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1 for success and 0 or a negative value for failure. In particular, a return
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value of -2 indicates the operation is not supported by the public key
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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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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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or 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_cleanup() 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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=head1 HISTORY
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EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
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were first added to 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 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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