202 lines
7 KiB
Text
202 lines
7 KiB
Text
=pod
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=head1 NAME
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EVP_DigestInit, EVP_DigestUpdate, EVP_DigestFinal, EVP_MAX_MD_SIZE,
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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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EVP digest routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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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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#define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
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int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
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#define EVP_MD_type(e) ((e)->type)
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#define EVP_MD_pkey_type(e) ((e)->pkey_type)
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#define EVP_MD_size(e) ((e)->md_size)
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#define EVP_MD_block_size(e) ((e)->block_size)
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#define EVP_MD_CTX_md(e) (e)->digest)
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#define EVP_MD_CTX_size(e) EVP_MD_size((e)->digest)
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#define EVP_MD_CTX_block_size(e) EVP_MD_block_size((e)->digest)
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#define EVP_MD_CTX_type(e) EVP_MD_type((e)->digest)
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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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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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=head1 DESCRIPTION
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The EVP digest routines are a high level interface to message digests.
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EVP_DigestInit() initializes a digest context B<ctx> to use a digest
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B<type>: this will typically be supplied by a function such as
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EVP_sha1().
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EVP_DigestUpdate() hashes B<cnt> bytes of data at B<d> into the
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digest context B<ctx>. This function can be called several times on the
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same B<ctx> to hash additional data.
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EVP_DigestFinal() retrieves the digest value from B<ctx> and places
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it in B<md>. If the B<s> parameter is not NULL 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 B<s>, at most B<EVP_MAX_MD_SIZE> bytes will be written.
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After calling EVP_DigestFinal() no additional calls to EVP_DigestUpdate()
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can be made, but EVP_DigestInit() can be called to initialize a new
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digest operation.
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EVP_MD_CTX_copy() can be used to copy the message digest state from
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B<in> to B<out>. 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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EVP_MD_size() and EVP_MD_CTX_size() return the size of the message digest
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when passed an B<EVP_MD> or an B<EVP_MD_CTX> structure, i.e. the size of the
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hash.
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EVP_MD_block_size() and EVP_MD_CTX_block_size() return the block size of the
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message digest when passed an B<EVP_MD> or an B<EVP_MD_CTX> structure.
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EVP_MD_type() and EVP_MD_CTX_type() return the NID of the OBJECT IDENTIFIER
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representing the given message digest when passed an B<EVP_MD> structure.
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For example EVP_MD_type(EVP_sha1()) returns B<NID_sha1>. This function is
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normally used when setting ASN1 OIDs.
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EVP_MD_CTX_md() returns the B<EVP_MD> structure corresponding to the passed
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B<EVP_MD_CTX>.
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EVP_MD_pkey_type() returns the NID of the public key signing algorithm associated
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with this digest. For example EVP_sha1() is associated with RSA so this will
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return B<NID_sha1WithRSAEncryption>. This "link" between digests and signature
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algorithms may not be retained in future versions of OpenSSL.
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EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_mdc2() and EVP_ripemd160()
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return B<EVP_MD> structures for the MD2, MD5, SHA, SHA1, MDC2 and RIPEMD160 digest
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algorithms respectively. The associated signature algorithm is RSA in each case.
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EVP_dss() and EVP_dss1() return B<EVP_MD> structures for SHA and SHA1 digest
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algorithms but using DSS (DSA) for the signature algorithm.
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EVP_md_null() is a "null" message digest that does nothing: i.e. the hash it
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returns is of zero length.
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EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
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return an B<EVP_MD> structure when passed a digest name, a digest NID or
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an ASN1_OBJECT structure respectively. The digest table must be initialized
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using, for example, OpenSSL_add_all_digests() for these functions to work.
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=head1 RETURN VALUES
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EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal() do not return values.
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EVP_MD_CTX_copy() returns 1 if successful or 0 for failure.
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EVP_MD_type(), EVP_MD_pkey_type() and EVP_MD_type() return the NID of the
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corresponding OBJECT IDENTIFIER or NID_undef if none exists.
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EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(e), EVP_MD_size(),
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EVP_MD_CTX_block_size() and EVP_MD_block_size() return the digest or block
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size in bytes.
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EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_dss(),
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EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return pointers to the
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corresponding EVP_MD structures.
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EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
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return either an B<EVP_MD> structure or NULL if an error occurs.
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=head1 NOTES
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The B<EVP> 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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SHA1 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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=head1 EXAMPLE
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This example digests the data "Test Message\n" and "Hello World\n", using the
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digest name passed on the command line.
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#include <stdio.h>
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#include <openssl/evp.h>
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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\n";
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char mess2[] = "Hello World\n";
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unsigned char md_value[EVP_MAX_MD_SIZE];
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int md_len, i;
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OpenSSL_add_all_digests();
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if(!argv[1]) {
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printf("Usage: mdtest digestname\n");
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exit(1);
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}
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md = EVP_get_digestbyname(argv[1]);
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if(!md) {
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printf("Unknown message digest %s\n", argv[1]);
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exit(1);
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}
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EVP_DigestInit(&mdctx, md);
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EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
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EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
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EVP_DigestFinal(&mdctx, md_value, &md_len);
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printf("Digest is: ");
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for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
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printf("\n");
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}
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=head1 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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The link between digests and signing algorithms results in a situation where
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EVP_sha1() must be used with RSA and EVP_dss1() must be used with DSS
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even though they are identical digests.
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The size of an B<EVP_MD_CTX> structure is determined at compile time: this results
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in code that must be recompiled if the size of B<EVP_MD_CTX> increases.
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=head1 SEE ALSO
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L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
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L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
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L<sha(3)|sha(3)>, L<digest(1)|digest(1)>
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=head1 HISTORY
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EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal() are
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available in all versions of SSLeay and OpenSSL.
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=cut
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