354 lines
12 KiB
Groff
354 lines
12 KiB
Groff
.\" $NetBSD: EVP_DigestInit.3,v 1.7 2002/02/07 09:24:08 ross Exp $
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.\" ======================================================================
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.\"
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.IX Title "EVP_DigestInit 3"
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.TH EVP_DigestInit 3 "0.9.6a" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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EVP_DigestInit, EVP_DigestUpdate, EVP_DigestFinal, \s-1EVP_MAX_MD_SIZE\s0,
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EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size,
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EVP_MD_CTX_md, EVP_MD_CTX_size, EVP_MD_CTX_block_size, EVP_MD_CTX_type,
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EVP_md_null, EVP_md2, EVP_md5, EVP_sha, EVP_sha1, EVP_dss, EVP_dss1, EVP_mdc2,
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EVP_ripemd160, EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj \-
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\&\s-1EVP\s0 digest routines
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include \*[Lt]openssl/evp.h\*[Gt]
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.Ve
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.Vb 4
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\& void EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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\& void EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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\& void EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
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\& unsigned int *s);
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.Ve
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.Vb 1
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\& #define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
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.Ve
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.Vb 1
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\& int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
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.Ve
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.Vb 4
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\& #define EVP_MD_type(e) ((e)-\*[Gt]type)
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\& #define EVP_MD_pkey_type(e) ((e)-\*[Gt]pkey_type)
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\& #define EVP_MD_size(e) ((e)-\*[Gt]md_size)
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\& #define EVP_MD_block_size(e) ((e)-\*[Gt]block_size)
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.Ve
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.Vb 4
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\& #define EVP_MD_CTX_md(e) (e)-\*[Gt]digest)
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\& #define EVP_MD_CTX_size(e) EVP_MD_size((e)-\*[Gt]digest)
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\& #define EVP_MD_CTX_block_size(e) EVP_MD_block_size((e)-\*[Gt]digest)
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\& #define EVP_MD_CTX_type(e) EVP_MD_type((e)-\*[Gt]digest)
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.Ve
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.Vb 9
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\& EVP_MD *EVP_md_null(void);
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\& EVP_MD *EVP_md2(void);
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\& EVP_MD *EVP_md5(void);
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\& EVP_MD *EVP_sha(void);
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\& EVP_MD *EVP_sha1(void);
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\& EVP_MD *EVP_dss(void);
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\& EVP_MD *EVP_dss1(void);
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\& EVP_MD *EVP_mdc2(void);
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\& EVP_MD *EVP_ripemd160(void);
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.Ve
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.Vb 3
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\& const EVP_MD *EVP_get_digestbyname(const char *name);
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\& #define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
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\& #define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
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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 digest routines are a high level interface to message digests.
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.PP
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\&\fIEVP_DigestInit()\fR initializes a digest context \fBctx\fR to use a digest
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\&\fBtype\fR: this will typically be supplied by a function such as
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\&\fIEVP_sha1()\fR.
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.PP
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\&\fIEVP_DigestUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
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digest context \fBctx\fR. This function can be called several times on the
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same \fBctx\fR to hash additional data.
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.PP
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\&\fIEVP_DigestFinal()\fR retrieves the digest value from \fBctx\fR and places
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it in \fBmd\fR. If the \fBs\fR parameter is not \s-1NULL\s0 then the number of
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bytes of data written (i.e. the length of the digest) will be written
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to the integer at \fBs\fR, at most \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes will be written.
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After calling \fIEVP_DigestFinal()\fR no additional calls to \fIEVP_DigestUpdate()\fR
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can be made, but \fIEVP_DigestInit()\fR can be called to initialize a new
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digest operation.
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.PP
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\&\fIEVP_MD_CTX_copy()\fR can be used to copy the message digest state from
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\&\fBin\fR to \fBout\fR. This is useful if large amounts of data are to be
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hashed which only differ in the last few bytes.
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.PP
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\&\fIEVP_MD_size()\fR and \fIEVP_MD_CTX_size()\fR return the size of the message digest
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when passed an \fB\s-1EVP_MD\s0\fR or an \fB\s-1EVP_MD_CTX\s0\fR structure, i.e. the size of the
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hash.
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.PP
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\&\fIEVP_MD_block_size()\fR and \fIEVP_MD_CTX_block_size()\fR return the block size of the
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message digest when passed an \fB\s-1EVP_MD\s0\fR or an \fB\s-1EVP_MD_CTX\s0\fR structure.
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.PP
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\&\fIEVP_MD_type()\fR and \fIEVP_MD_CTX_type()\fR return the \s-1NID\s0 of the \s-1OBJECT\s0 \s-1IDENTIFIER\s0
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representing the given message digest when passed an \fB\s-1EVP_MD\s0\fR structure.
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For example EVP_MD_type(\fIEVP_sha1()\fR) returns \fBNID_sha1\fR. This function is
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normally used when setting \s-1ASN1\s0 OIDs.
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.PP
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\&\fIEVP_MD_CTX_md()\fR returns the \fB\s-1EVP_MD\s0\fR structure corresponding to the passed
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\&\fB\s-1EVP_MD_CTX\s0\fR.
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.PP
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\&\fIEVP_MD_pkey_type()\fR returns the \s-1NID\s0 of the public key signing algorithm associated
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with this digest. For example \fIEVP_sha1()\fR is associated with \s-1RSA\s0 so this will
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return \fBNID_sha1WithRSAEncryption\fR. This \*(L"link\*(R" between digests and signature
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algorithms may not be retained in future versions of OpenSSL.
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.PP
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\&\fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR
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return \fB\s-1EVP_MD\s0\fR structures for the \s-1MD2\s0, \s-1MD5\s0, \s-1SHA\s0, \s-1SHA1\s0, \s-1MDC2\s0 and \s-1RIPEMD160\s0 digest
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algorithms respectively. The associated signature algorithm is \s-1RSA\s0 in each case.
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.PP
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\&\fIEVP_dss()\fR and \fIEVP_dss1()\fR return \fB\s-1EVP_MD\s0\fR structures for \s-1SHA\s0 and \s-1SHA1\s0 digest
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algorithms but using \s-1DSS\s0 (\s-1DSA\s0) for the signature algorithm.
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.PP
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\&\fIEVP_md_null()\fR is a \*(L"null\*(R" message digest that does nothing: i.e. the hash it
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returns is of zero length.
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.PP
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\&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR
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return an \fB\s-1EVP_MD\s0\fR structure when passed a digest name, a digest \s-1NID\s0 or
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an \s-1ASN1_OBJECT\s0 structure respectively. The digest table must be initialized
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using, for example, \fIOpenSSL_add_all_digests()\fR for these functions to work.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal()\fR do not return values.
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.PP
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\&\fIEVP_MD_CTX_copy()\fR returns 1 if successful or 0 for failure.
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.PP
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\&\fIEVP_MD_type()\fR, \fIEVP_MD_pkey_type()\fR and \fIEVP_MD_type()\fR return the \s-1NID\s0 of the
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corresponding \s-1OBJECT\s0 \s-1IDENTIFIER\s0 or NID_undef if none exists.
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.PP
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\&\fIEVP_MD_size()\fR, \fIEVP_MD_block_size()\fR, \fIEVP_MD_CTX_size\fR\|(e), \fIEVP_MD_size()\fR,
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\&\fIEVP_MD_CTX_block_size()\fR and \fIEVP_MD_block_size()\fR return the digest or block
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size in bytes.
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.PP
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\&\fIEVP_md_null()\fR, \fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_dss()\fR,
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\&\fIEVP_dss1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR return pointers to the
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corresponding \s-1EVP_MD\s0 structures.
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.PP
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\&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR
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return either an \fB\s-1EVP_MD\s0\fR structure or \s-1NULL\s0 if an error occurs.
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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 message digests 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 digest used and much more flexible.
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.PP
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\&\s-1SHA1\s0 is the digest of choice for new applications. The other digest algorithms
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are still in common use.
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.SH "EXAMPLE"
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.IX Header "EXAMPLE"
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This example digests the data \*(L"Test Message\en\*(R" and \*(L"Hello World\en\*(R", using the
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digest name passed on the command line.
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.PP
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.Vb 2
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\& #include \*[Lt]stdio.h\*[Gt]
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\& #include \*[Lt]openssl/evp.h\*[Gt]
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.Ve
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.Vb 8
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\& main(int argc, char *argv[])
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\& {
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\& EVP_MD_CTX mdctx;
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\& const EVP_MD *md;
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\& char mess1[] = "Test Message\en";
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\& char mess2[] = "Hello World\en";
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\& unsigned char md_value[EVP_MAX_MD_SIZE];
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\& int md_len, i;
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.Ve
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.Vb 1
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\& OpenSSL_add_all_digests();
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.Ve
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.Vb 4
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\& if(!argv[1]) {
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\& printf("Usage: mdtest digestname\en");
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\& exit(1);
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\& }
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.Ve
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.Vb 1
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\& md = EVP_get_digestbyname(argv[1]);
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.Ve
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.Vb 4
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\& if(!md) {
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\& printf("Unknown message digest %s\en", argv[1]);
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\& exit(1);
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\& }
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.Ve
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.Vb 4
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\& EVP_DigestInit(\*[Am]mdctx, md);
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\& EVP_DigestUpdate(\*[Am]mdctx, mess1, strlen(mess1));
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\& EVP_DigestUpdate(\*[Am]mdctx, mess2, strlen(mess2));
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\& EVP_DigestFinal(\*[Am]mdctx, md_value, \*[Am]md_len);
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.Ve
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.Vb 4
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\& printf("Digest is: ");
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\& for(i = 0; i \*[Lt] md_len; i++) printf("%02x", md_value[i]);
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\& printf("\en");
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\& }
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.Ve
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.SH "BUGS"
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.IX Header "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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.PP
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The link between digests and signing algorithms results in a situation where
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\&\fIEVP_sha1()\fR must be used with \s-1RSA\s0 and \fIEVP_dss1()\fR must be used with \s-1DSS\s0
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even though they are identical digests.
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.PP
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The size of an \fB\s-1EVP_MD_CTX\s0\fR structure is determined at compile time: this results
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in code that must be recompiled if the size of \fB\s-1EVP_MD_CTX\s0\fR increases.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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openssl_evp(3), openssl_hmac(3), md2(3),
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openssl_md5(3), openssl_mdc2(3), openssl_ripemd(3),
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openssl_sha(3), digest(1)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal()\fR are
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available in all versions of SSLeay and OpenSSL.
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