232 lines
7.3 KiB
Groff
232 lines
7.3 KiB
Groff
.\" Automatically generated by Pod::Man version 1.15
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.\" Wed Feb 19 16:42:54 2003
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.\" ======================================================================
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.\"
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.IX Title "EVP_SignInit 3"
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.TH EVP_SignInit 3 "0.9.7a" "2003-02-19" "OpenSSL"
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.UC
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.SH "NAME"
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EVP_SignInit, EVP_SignUpdate, EVP_SignFinal \- \s-1EVP\s0 signing functions
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/evp.h>
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.Ve
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.Vb 3
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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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.Ve
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.Vb 1
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\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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.Ve
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.Vb 1
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\& int EVP_PKEY_size(EVP_PKEY *pkey);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \s-1EVP\s0 signature routines are a high level interface to digital
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signatures.
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.PP
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\&\fIEVP_SignInit_ex()\fR sets up signing context \fBctx\fR to use digest
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\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized with
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\&\fIEVP_MD_CTX_init()\fR before calling this function.
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.PP
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\&\fIEVP_SignUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
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signature context \fBctx\fR. This function can be called several times on the
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same \fBctx\fR to include additional data.
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.PP
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\&\fIEVP_SignFinal()\fR signs the data in \fBctx\fR using the private key \fBpkey\fR
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and places the signature in \fBsig\fR. If the \fBs\fR parameter is not \s-1NULL\s0
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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 \fBs\fR, at most EVP_PKEY_size(pkey) bytes
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will be written.
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.PP
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\&\fIEVP_SignInit()\fR initializes a signing context \fBctx\fR to use the default
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implementation of digest \fBtype\fR.
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.PP
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\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes. The actual
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signature returned by \fIEVP_SignFinal()\fR may be smaller.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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for success and 0 for failure.
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.PP
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\&\fIEVP_PKEY_size()\fR returns the maximum size of a signature in bytes.
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.PP
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The error codes can be obtained by ERR_get_error(3).
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.SH "NOTES"
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.IX Header "NOTES"
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The \fB\s-1EVP\s0\fR 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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.PP
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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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EVP_DigestInit(3).
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.PP
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When signing with \s-1DSA\s0 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 \s-1RSA\s0 signatures.
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.PP
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The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
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This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
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later to digest and sign additional data.
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.PP
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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 \fIEVP_MD_CTX_cleanup()\fR or a memory leak
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will occur.
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.SH "BUGS"
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.IX Header "BUGS"
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Older versions of this documentation wrongly stated that calls to
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\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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EVP_VerifyInit(3),
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EVP_DigestInit(3), err(3),
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evp(3), hmac(3), md2(3),
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md5(3), mdc2(3), ripemd(3),
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sha(3), dgst(1)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIEVP_SignInit()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR are
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available in all versions of SSLeay and OpenSSL.
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.PP
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\&\fIEVP_SignInit_ex()\fR was added in OpenSSL 0.9.7.
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