.\" $NetBSD: EVP_DigestInit.3,v 1.13 2003/07/24 14:16:40 itojun Exp $ .\" .\" Automatically generated by Pod::Man version 1.02 .\" Thu Jul 24 13:07:56 2003 .\" .\" Standard preamble: .\" ====================================================================== .de Sh \" Subsection heading .br .if t .Sp .ne 5 .PP \fB\\$1\fR .PP .. .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Ip \" List item .br .ie \\n(.$>=3 .ne \\$3 .el .ne 3 .IP "\\$1" \\$2 .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" 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++. 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If \fBimpl\fR is \s-1NULL\s0 then the default implementation of digest \fBtype\fR is used. .PP \&\fIEVP_DigestUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the digest context \fBctx\fR. This function can be called several times on the same \fBctx\fR to hash additional data. .PP \&\fIEVP_DigestFinal_ex()\fR retrieves the digest value from \fBctx\fR and places it in \fBmd\fR. If the \fBs\fR 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 \fBs\fR, at most \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes will be written. After calling \fIEVP_DigestFinal_ex()\fR no additional calls to \fIEVP_DigestUpdate()\fR can be made, but \fIEVP_DigestInit_ex()\fR can be called to initialize a new digest operation. .PP \&\fIEVP_MD_CTX_cleanup()\fR cleans up digest context \fBctx\fR, it should be called after a digest context is no longer needed. .PP \&\fIEVP_MD_CTX_destroy()\fR cleans up digest context \fBctx\fR and frees up the space allocated to it, it should be called only on a context created using \fIEVP_MD_CTX_create()\fR. .PP \&\fIEVP_MD_CTX_copy_ex()\fR can be used to copy the message digest state from \&\fBin\fR to \fBout\fR. This is useful if large amounts of data are to be hashed which only differ in the last few bytes. \fBout\fR must be initialized before calling this function. .PP \&\fIEVP_DigestInit()\fR behaves in the same way as \fIEVP_DigestInit_ex()\fR except the passed context \fBctx\fR does not have to be initialized, and it always uses the default digest implementation. .PP \&\fIEVP_DigestFinal()\fR is similar to \fIEVP_DigestFinal_ex()\fR except the digest contet \fBctx\fR is automatically cleaned up. .PP \&\fIEVP_MD_CTX_copy()\fR is similar to \fIEVP_MD_CTX_copy_ex()\fR except the destination \&\fBout\fR does not have to be initialized. .PP \&\fIEVP_MD_size()\fR and \fIEVP_MD_CTX_size()\fR return the size of the message digest 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 hash. .PP \&\fIEVP_MD_block_size()\fR and \fIEVP_MD_CTX_block_size()\fR return the block size of the message digest when passed an \fB\s-1EVP_MD\s0\fR or an \fB\s-1EVP_MD_CTX\s0\fR structure. .PP \&\fIEVP_MD_type()\fR and \fIEVP_MD_CTX_type()\fR return the \s-1NID\s0 of the \s-1OBJECT\s0 \s-1IDENTIFIER\s0 representing the given message digest when passed an \fB\s-1EVP_MD\s0\fR structure. For example EVP_MD_type(\fIEVP_sha1()\fR) returns \fBNID_sha1\fR. This function is normally used when setting \s-1ASN1\s0 OIDs. .PP \&\fIEVP_MD_CTX_md()\fR returns the \fB\s-1EVP_MD\s0\fR structure corresponding to the passed \&\fB\s-1EVP_MD_CTX\s0\fR. .PP \&\fIEVP_MD_pkey_type()\fR returns the \s-1NID\s0 of the public key signing algorithm associated with this digest. For example \fIEVP_sha1()\fR is associated with \s-1RSA\s0 so this will return \fBNID_sha1WithRSAEncryption\fR. This \*(L"link\*(R" between digests and signature algorithms may not be retained in future versions of OpenSSL. .PP \&\fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR 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 algorithms respectively. The associated signature algorithm is \s-1RSA\s0 in each case. .PP \&\fIEVP_dss()\fR and \fIEVP_dss1()\fR return \fB\s-1EVP_MD\s0\fR structures for \s-1SHA\s0 and \s-1SHA1\s0 digest algorithms but using \s-1DSS\s0 (\s-1DSA\s0) for the signature algorithm. .PP \&\fIEVP_md_null()\fR is a \*(L"null\*(R" message digest that does nothing: i.e. the hash it returns is of zero length. .PP \&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR return an \fB\s-1EVP_MD\s0\fR 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, \fIOpenSSL_add_all_digests()\fR for these functions to work. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fIEVP_DigestInit_ex()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal_ex()\fR return 1 for success and 0 for failure. .PP \&\fIEVP_MD_CTX_copy_ex()\fR returns 1 if successful or 0 for failure. .PP \&\fIEVP_MD_type()\fR, \fIEVP_MD_pkey_type()\fR and \fIEVP_MD_type()\fR return the \s-1NID\s0 of the corresponding \s-1OBJECT\s0 \s-1IDENTIFIER\s0 or NID_undef if none exists. .PP \&\fIEVP_MD_size()\fR, \fIEVP_MD_block_size()\fR, \fIEVP_MD_CTX_size\fR\|(e), \fIEVP_MD_size()\fR, \&\fIEVP_MD_CTX_block_size()\fR and \fIEVP_MD_block_size()\fR return the digest or block size in bytes. .PP \&\fIEVP_md_null()\fR, \fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_dss()\fR, \&\fIEVP_dss1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR return pointers to the corresponding \s-1EVP_MD\s0 structures. .PP \&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR return either an \fB\s-1EVP_MD\s0\fR structure or \s-1NULL\s0 if an error occurs. .SH "NOTES" .IX Header "NOTES" The \fB\s-1EVP\s0\fR interface to message digests should almost always be used in preference to the low level interfaces. This is because the code then becomes transparent to the digest used and much more flexible. .PP \&\s-1SHA1\s0 is the digest of choice for new applications. The other digest algorithms are still in common use. .PP For most applications the \fBimpl\fR parameter to \fIEVP_DigestInit_ex()\fR will be set to \s-1NULL\s0 to use the default digest implementation. .PP The functions \fIEVP_DigestInit()\fR, \fIEVP_DigestFinal()\fR and \fIEVP_MD_CTX_copy()\fR are obsolete but are retained to maintain compatibility with existing code. New applications should use \fIEVP_DigestInit_ex()\fR, \fIEVP_DigestFinal_ex()\fR and \&\fIEVP_MD_CTX_copy_ex()\fR because they can efficiently reuse a digest context instead of initializing and cleaning it up on each call and allow non default implementations of digests to be specified. .PP In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use memory leaks will occur. .SH "EXAMPLE" .IX Header "EXAMPLE" This example digests the data \*(L"Test Message\en\*(R" and \*(L"Hello World\en\*(R", using the digest name passed on the command line. .PP .Vb 2 \& #include \& #include .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 6 \& EVP_MD_CTX_init(&mdctx); \& EVP_DigestInit_ex(&mdctx, md, NULL); \& EVP_DigestUpdate(&mdctx, mess1, strlen(mess1)); \& EVP_DigestUpdate(&mdctx, mess2, strlen(mess2)); \& EVP_DigestFinal_ex(&mdctx, md_value, &md_len); \& EVP_MD_CTX_cleanup(&mdctx); .Ve .Vb 4 \& printf("Digest is: "); \& for(i = 0; i < md_len; i++) printf("%02x", md_value[i]); \& printf("\en"); \& } .Ve .SH "BUGS" .IX Header "BUGS" The link between digests and signing algorithms results in a situation where \&\fIEVP_sha1()\fR must be used with \s-1RSA\s0 and \fIEVP_dss1()\fR must be used with \s-1DSS\s0 even though they are identical digests. .SH "SEE ALSO" .IX Header "SEE ALSO" openssl_evp(3), openssl_hmac(3), md2(3), openssl_md5(3), openssl_mdc2(3), openssl_ripemd(3), openssl_sha(3), openssl_dgst(1) .SH "HISTORY" .IX Header "HISTORY" \&\fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal()\fR are available in all versions of SSLeay and OpenSSL. .PP \&\fIEVP_MD_CTX_init()\fR, \fIEVP_MD_CTX_create()\fR, \fIEVP_MD_CTX_copy_ex()\fR, \&\fIEVP_MD_CTX_cleanup()\fR, \fIEVP_MD_CTX_destroy()\fR, \fIEVP_DigestInit_ex()\fR and \fIEVP_DigestFinal_ex()\fR were added in OpenSSL 0.9.7. .PP \&\fIEVP_md_null()\fR, \fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \&\fIEVP_dss()\fR, \fIEVP_dss1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR were changed to return truely const \s-1EVP_MD\s0 * in OpenSSL 0.9.7.