Tue Jul 30 09:21:40 2002
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.... Set up some character translations and predefined strings. \*(-- will
give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
double quote, and \*(R" will give a right double quote. | will give a
real vertical bar. \*(C+ will give a nicer C++. Capital omega is used
to do unbreakable dashes and therefore won't be available. \*(C` and
\*(C' expand to `' in nroff, nothing in troff, for use with C<>
.tr \(*W-|\(bv\*(Tr . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' 'br\}
If the F register is turned on, we'll generate index entries on stderr
for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
index entries marked with X<> in POD. Of course, you'll have to process
the output yourself in some meaningful fashion.
. de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . nr % 0 . rr F .\}
For nroff, turn off justification. Always turn off hyphenation; it
makes way too many mistakes in technical documents.
Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
Fear. Run. Save yourself. No user-serviceable parts.
.bd B 3 . \" fudge factors for nroff and troff . ds #H 0 . ds #V .8m . ds #F .3m . ds #[ \f1 . ds #] .\} . ds #H ((1u-(\\\\n(.fu%2u))*.13m) . ds #V .6m . ds #F 0 . ds #[ \& . ds #] \& .\} . \" simple accents for nroff and troff . ds ' \& . ds ` \& . ds ^ \& . ds , \& . ds ~ ~ . ds / .\} . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' .\} . \" troff and (daisy-wheel) nroff accents . \" corrections for vroff . \" for low resolution devices (crt and lpr) \{\ . ds : e . ds 8 ss . ds o a . ds d- d\h'-1'\(ga . ds D- D\h'-1'\(hy . ds th \o'bp' . ds Th \o'LP' . ds ae ae . ds Ae AE .\} ======================================================================
Title "EVP_DigestInit 3"
\fIEVP_DigestInit() initializes a digest context ctx to use a digest \fBtype: this will typically be supplied by a function such as \fIEVP_sha1().
\fIEVP_DigestUpdate() hashes cnt bytes of data at d into the digest context ctx. This function can be called several times on the same ctx to hash additional data.
\fIEVP_DigestFinal() retrieves the digest value from ctx and places it in md. If the s parameter is not \s-1NULL\s0 then the number of bytes of data written (i.e. the length of the digest) will be written to the integer at s, at most \s-1EVP_MAX_MD_SIZE\s0 bytes will be written. After calling EVP_DigestFinal() no additional calls to EVP_DigestUpdate() can be made, but EVP_DigestInit() can be called to initialize a new digest operation.
\fIEVP_MD_CTX_copy() can be used to copy the message digest state from \fBin to out. This is useful if large amounts of data are to be hashed which only differ in the last few bytes.
\fIEVP_MD_size() and EVP_MD_CTX_size() return the size of the message digest when passed an \s-1EVP_MD\s0 or an \s-1EVP_MD_CTX\s0 structure, i.e. the size of the hash.
\fIEVP_MD_block_size() and EVP_MD_CTX_block_size() return the block size of the message digest when passed an \s-1EVP_MD\s0 or an \s-1EVP_MD_CTX\s0 structure.
\fIEVP_MD_type() and EVP_MD_CTX_type() return the \s-1NID\s0 of the \s-1OBJECT\s0 \s-1IDENTIFIER\s0 representing the given message digest when passed an \s-1EVP_MD\s0 structure. For example EVP_MD_type(EVP_sha1()) returns NID_sha1. This function is normally used when setting \s-1ASN1\s0 OIDs.
\fIEVP_MD_CTX_md() returns the \s-1EVP_MD\s0 structure corresponding to the passed \fB\s-1EVP_MD_CTX\s0.
\fIEVP_MD_pkey_type() returns the \s-1NID\s0 of the public key signing algorithm associated with this digest. For example EVP_sha1() is associated with \s-1RSA\s0 so this will return NID_sha1WithRSAEncryption. This \*(L"link\*(R" between digests and signature algorithms may not be retained in future versions of OpenSSL.
\fIEVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_mdc2() and EVP_ripemd160() return \s-1EVP_MD\s0 structures for the \s-1MD2\s0, \s-1MD5\s0, \s-1SHA\s0, \s-1SHA1\s0, \s-1MDC2\s0 and \s-1RIPEMD160\s0 digest algorithms respectively. The associated signature algorithm is \s-1RSA\s0 in each case.
\fIEVP_dss() and EVP_dss1() return \s-1EVP_MD\s0 structures for \s-1SHA\s0 and \s-1SHA1\s0 digest algorithms but using \s-1DSS\s0 (\s-1DSA\s0) for the signature algorithm.
\fIEVP_md_null() is a \*(L"null\*(R" message digest that does nothing: i.e. the hash it returns is of zero length.
\fIEVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj() return an \s-1EVP_MD\s0 structure when passed a digest name, a digest \s-1NID\s0 or an \s-1ASN1_OBJECT\s0 structure respectively. The digest table must be initialized using, for example, OpenSSL_add_all_digests() for these functions to work.
\fIEVP_MD_CTX_copy() returns 1 if successful or 0 for failure.
\fIEVP_MD_type(), EVP_MD_pkey_type() and EVP_MD_type() return the \s-1NID\s0 of the corresponding \s-1OBJECT\s0 \s-1IDENTIFIER\s0 or NID_undef if none exists.
\fIEVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size\|(e), EVP_MD_size(), \fIEVP_MD_CTX_block_size() and EVP_MD_block_size() return the digest or block size in bytes.
\fIEVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_dss(), \fIEVP_dss1(), EVP_mdc2() and EVP_ripemd160() return pointers to the corresponding \s-1EVP_MD\s0 structures.
\fIEVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj() return either an \s-1EVP_MD\s0 structure or \s-1NULL\s0 if an error occurs.
\s-1SHA1\s0 is the digest of choice for new applications. The other digest algorithms are still in common use.
.Vb 2 #include <stdio.h> #include <openssl/evp.h> .Ve .Vb 8 main(int argc, char *argv[]) { EVP_MD_CTX mdctx; const EVP_MD *md; char mess1[] = "Test Message\en"; char mess2[] = "Hello World\en"; unsigned char md_value[EVP_MAX_MD_SIZE]; int md_len, i; .Ve .Vb 1 OpenSSL_add_all_digests(); .Ve .Vb 4 if(!argv[1]) { printf("Usage: mdtest digestname\en"); exit(1); } .Ve .Vb 1 md = EVP_get_digestbyname(argv[1]); .Ve .Vb 4 if(!md) { printf("Unknown message digest %s\en", argv[1]); exit(1); } .Ve .Vb 4 EVP_DigestInit(&mdctx, md); EVP_DigestUpdate(&mdctx, mess1, strlen(mess1)); EVP_DigestUpdate(&mdctx, mess2, strlen(mess2)); EVP_DigestFinal(&mdctx, md_value, &md_len); .Ve .Vb 4 printf("Digest is: "); for(i = 0; i < md_len; i++) printf("%02x", md_value[i]); printf("\en"); } .Ve
The link between digests and signing algorithms results in a situation where \fIEVP_sha1() must be used with \s-1RSA\s0 and EVP_dss1() must be used with \s-1DSS\s0 even though they are identical digests.
The size of an \s-1EVP_MD_CTX\s0 structure is determined at compile time: this results in code that must be recompiled if the size of \s-1EVP_MD_CTX\s0 increases.