86 lines
2.9 KiB
Plaintext
86 lines
2.9 KiB
Plaintext
=pod
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=head1 NAME
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EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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void 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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int EVP_PKEY_size(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() initializes a signing context B<ctx> to using digest
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B<type>: this will typically be supplied by a function such as
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EVP_sha1().
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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>
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and places the signature in B<sig>. If the B<s> parameter is not NULL
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then 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. After calling EVP_SignFinal() no additional calls to
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EVP_SignUpdate() can be made, but EVP_SignInit() can be called to initialize
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a new signature operation.
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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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=head1 RETURN VALUES
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EVP_SignInit() and EVP_SignUpdate() do not return values.
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EVP_SignFinal() returns 1 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)|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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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)|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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=head1 BUGS
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Several of the functions do not return values: maybe they should. Although the
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internal digest operations will never fail some future hardware based operations
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might.
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=head1 SEE ALSO
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L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
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L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
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L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
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L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
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L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
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=head1 HISTORY
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EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
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available in all versions of SSLeay and OpenSSL.
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=cut
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