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.tr \(*W- . 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" '' . ds C` . ds C' 'br\}
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Title "EVP_DigestInit 3"
way too many mistakes in technical documents.
\fIEVP_MD_CTX_init() initializes digest context ctx.
\fIEVP_MD_CTX_create() allocates, initializes and returns a digest context.
\fIEVP_DigestInit_ex() sets up digest context ctx to use a digest \fBtype from \s-1ENGINE \s0impl. ctx must be initialized before calling this function. type will typically be supplied by a functionsuch as EVP_sha1(). If impl is \s-1NULL\s0 then the default implementation of digest type is used.
\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_ex() 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_ex() no additional calls to EVP_DigestUpdate() can be made, but EVP_DigestInit_ex() can be called to initialize a new digest operation.
\fIEVP_MD_CTX_cleanup() cleans up digest context ctx, it should be called after a digest context is no longer needed.
\fIEVP_MD_CTX_destroy() cleans up digest context ctx and frees up the space allocated to it, it should be called only on a context created using EVP_MD_CTX_create().
\fIEVP_MD_CTX_copy_ex() 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. out must be initialized before calling this function.
\fIEVP_DigestInit() behaves in the same way as EVP_DigestInit_ex() except the passed context ctx does not have to be initialized, and it always uses the default digest implementation.
\fIEVP_DigestFinal() is similar to EVP_DigestFinal_ex() except the digest context ctx is automatically cleaned up.
\fIEVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except the destination \fBout does not have to be initialized.
\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 IDENTIFIER\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. Since digests and signature algorithms are no longer linked this function is only retained for compatibility reasons.
\fIEVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_sha224(), EVP_sha256(), \fIEVP_sha384(), EVP_sha512(), EVP_mdc2() and EVP_ripemd160() return \s-1EVP_MD\s0 structures for the \s-1MD2, MD5, SHA, SHA1, SHA224, SHA256, SHA384, SHA512, MDC2\s0 and \s-1RIPEMD160\s0 digest algorithms respectively.
\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. Note: there is no need to use these pseudo-digests in OpenSSL 1.0.0 and later, they are however retained for compatibility.
\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_ex() 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 IDENTIFIER\s0 or NID_undef if none exists.
\fIEVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size() and \fIEVP_MD_CTX_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.
New applications should use the \s-1SHA2\s0 digest algorithms such as \s-1SHA256.\s0 The other digest algorithms are still in common use.
For most applications the impl parameter to EVP_DigestInit_ex() will be set to \s-1NULL\s0 to use the default digest implementation.
The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy() are obsolete but are retained to maintain compatibility with existing code. New applications should use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and \fIEVP_MD_CTX_copy_ex() 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.
In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use memory leaks will occur.
Stack allocation of \s-1EVP_MD_CTX\s0 structures is common, for example:
.Vb 2 EVP_MD_CTX mctx; EVP_MD_CTX_init(&mctx); .Ve
This will cause binary compatibility issues if the size of \s-1EVP_MD_CTX\s0 structure changes (this will only happen with a major release of OpenSSL). Applications wishing to avoid this should use EVP_MD_CTX_create() instead:
.Vb 2 EVP_MD_CTX *mctx; mctx = EVP_MD_CTX_create(); .Ve
.Vb 2 #include <stdio.h> #include <openssl/evp.h> \& 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; \& OpenSSL_add_all_digests(); \& if(!argv[1]) { printf("Usage: mdtest digestname\en"); exit(1); } \& md = EVP_get_digestbyname(argv[1]); \& if(!md) { printf("Unknown message digest %s\en", argv[1]); exit(1); } \& mdctx = EVP_MD_CTX_create(); 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_destroy(mdctx); \& printf("Digest is: "); for(i = 0; i < md_len; i++) printf("%02x", md_value[i]); printf("\en"); \& /* Call this once before exit. */ EVP_cleanup(); exit(0); } .Ve
\fIEVP_MD_CTX_init(), EVP_MD_CTX_create(), EVP_MD_CTX_copy_ex(), \fIEVP_MD_CTX_cleanup(), EVP_MD_CTX_destroy(), EVP_DigestInit_ex() and EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.
\fIEVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), \fIEVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() were changed to return truely const \s-1EVP_MD\s0 * in OpenSSL 0.9.7.
The link between digests and signing algorithms was fixed in OpenSSL 1.0 and later, so now EVP_sha1() can be used with \s-1RSA\s0 and \s-1DSA\s0; there is no need to use EVP_dss1() any more.
OpenSSL 1.0 and later does not include the \s-1MD2\s0 digest algorithm in the default configuration due to its security weaknesses.