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.\" ======================================================================== |
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.\" |
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.IX Title "EVP_DigestSignInit 3" |
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.TH EVP_DigestSignInit 3 "2018-11-20" "1.0.2q" "OpenSSL" |
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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.\" way too many mistakes in technical documents. |
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.if n .ad l |
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.nh |
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.SH "NAME" |
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EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal \- EVP 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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\& |
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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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.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 signatures. |
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.PP |
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\&\fIEVP_DigestSignInit()\fR sets up signing context \fBctx\fR to use digest \fBtype\fR from |
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\&\s-1ENGINE\s0 \fBimpl\fR and private key \fBpkey\fR. \fBctx\fR must be initialized with |
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\&\fIEVP_MD_CTX_init()\fR before calling this function. If \fBpctx\fR is not \s-1NULL,\s0 the |
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\&\s-1EVP_PKEY_CTX\s0 of the signing operation will be written to \fB*pctx\fR: this can |
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be used to set alternative signing options. Note that any existing value in |
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\&\fB*pctx\fR is overwritten. The \s-1EVP_PKEY_CTX\s0 value returned must not be freed |
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directly by the application (it will be freed automatically when the \s-1EVP_MD_CTX\s0 |
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is freed). The digest \fBtype\fR may be \s-1NULL\s0 if the signing algorithm supports it. |
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.PP |
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\&\fIEVP_DigestSignUpdate()\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. This function is currently implemented |
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usig a macro. |
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.PP |
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\&\fIEVP_DigestSignFinal()\fR signs the data in \fBctx\fR places the signature in \fBsig\fR. |
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If \fBsig\fR is \fB\s-1NULL\s0\fR then the maximum size of the output buffer is written to |
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the \fBsiglen\fR parameter. If \fBsig\fR is not \fB\s-1NULL\s0\fR then before the call the |
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\&\fBsiglen\fR parameter should contain the length of the \fBsig\fR buffer, if the |
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call is successful the signature is written to \fBsig\fR and the amount of data |
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written to \fBsiglen\fR. |
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.SH "RETURN VALUES" |
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.IX Header "RETURN VALUES" |
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\&\fIEVP_DigestSignInit()\fR \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignaFinal()\fR 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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.PP |
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The error codes can be obtained from \fIERR_get_error\fR\|(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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In previous versions of OpenSSL there was a link between message digest types |
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and public key algorithms. This meant that \*(L"clone\*(R" digests such as \fIEVP_dss1()\fR |
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needed to be used to sign using \s-1SHA1\s0 and \s-1DSA.\s0 This is no longer necessary and |
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the use of clone digest is now discouraged. |
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.PP |
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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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.PP |
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The call to \fIEVP_DigestSignFinal()\fR internally finalizes a copy of the digest |
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context. This means that calls to \fIEVP_DigestSignUpdate()\fR and |
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\&\fIEVP_DigestSignFinal()\fR can be called 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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.PP |
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The use of \fIEVP_PKEY_size()\fR 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 \fIEVP_PKEY_size()\fR 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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.SH "SEE ALSO" |
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.IX Header "SEE ALSO" |
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\&\fIEVP_DigestVerifyInit\fR\|(3), |
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\&\fIEVP_DigestInit\fR\|(3), \fIerr\fR\|(3), |
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\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3), |
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\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3), |
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\&\fIsha\fR\|(3), \fIdgst\fR\|(1) |
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.SH "HISTORY" |
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.IX Header "HISTORY" |
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\&\fIEVP_DigestSignInit()\fR, \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignFinal()\fR |
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were first added to OpenSSL 1.0.0. |
