mirror of https://github.com/openssl/openssl
262 lines
9.3 KiB
Plaintext
262 lines
9.3 KiB
Plaintext
=pod
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=head1 NAME
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EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy_ex,
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EVP_DigestInit_ex, EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_MAX_MD_SIZE,
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EVP_DigestInit, EVP_DigestFinal, EVP_MD_CTX_copy, EVP_MD_type,
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EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,
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EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null, EVP_md2, EVP_md5, EVP_sha1,
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EVP_sha224, EVP_sha256, EVP_sha384, EVP_sha512, EVP_mdc2,
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EVP_ripemd160, EVP_blake2b, EVP_blake2s, EVP_get_digestbyname,
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EVP_get_digestbynid, EVP_get_digestbyobj - EVP digest routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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EVP_MD_CTX *EVP_MD_CTX_new(void);
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int EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
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void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
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int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
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unsigned int *s);
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int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);
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int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
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unsigned int *s);
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int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
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#define EVP_MAX_MD_SIZE 64 /* SHA512 */
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int EVP_MD_type(const EVP_MD *md);
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int EVP_MD_pkey_type(const EVP_MD *md);
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int EVP_MD_size(const EVP_MD *md);
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int EVP_MD_block_size(const EVP_MD *md);
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const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
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int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,
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const void *data, size_t count);
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void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
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int (*update) (EVP_MD_CTX *ctx,
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const void *data, size_t count));
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int EVP_MD_CTX_size(const EVP_MD *ctx);
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int EVP_MD_CTX_block_size(const EVP_MD *ctx);
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int EVP_MD_CTX_type(const EVP_MD *ctx);
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EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);
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void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);
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const EVP_MD *EVP_md_null(void);
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const EVP_MD *EVP_md2(void);
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const EVP_MD *EVP_md5(void);
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const EVP_MD *EVP_sha1(void);
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const EVP_MD *EVP_mdc2(void);
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const EVP_MD *EVP_ripemd160(void);
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const EVP_MD *EVP_blake2b(void);
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const EVP_MD *EVP_blake2s(void);
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const EVP_MD *EVP_sha224(void);
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const EVP_MD *EVP_sha256(void);
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const EVP_MD *EVP_sha384(void);
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const EVP_MD *EVP_sha512(void);
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const EVP_MD *EVP_get_digestbyname(const char *name);
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const EVP_MD *EVP_get_digestbynid(int type);
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const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);
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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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and should be used instead of the cipher-specific functions.
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EVP_MD_CTX_new() allocates, initializes and returns a digest context.
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EVP_MD_CTX_reset() resets the digest context B<ctx>. This can be used
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to reuse an already existing context.
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EVP_MD_CTX_free() cleans up digest context B<ctx> and frees up the
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space allocated to it.
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EVP_DigestInit_ex() sets up digest context B<ctx> to use a digest
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B<type> from ENGINE B<impl>. B<ctx> must be initialized before calling this
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function. B<type> will typically be supplied by a function such as EVP_sha1().
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If B<impl> is NULL then the default implementation of digest B<type> is used.
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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_ex() 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_ex() no additional calls to EVP_DigestUpdate()
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can be made, but EVP_DigestInit_ex() can be called to initialize a new
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digest operation.
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EVP_MD_CTX_copy_ex() 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. B<out> must be initialized
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before calling this function.
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EVP_DigestInit() behaves in the same way as EVP_DigestInit_ex() except
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the passed context B<ctx> does not have to be initialized, and it always
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uses the default digest implementation.
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EVP_DigestFinal() is similar to EVP_DigestFinal_ex() except the digest
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context B<ctx> is automatically cleaned up.
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EVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except the destination
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B<out> does not have to be initialized.
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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>. Since digests and signature algorithms
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are no longer linked this function is only retained for compatibility
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reasons.
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EVP_md2(), EVP_md5(), EVP_sha1(), EVP_sha224(), EVP_sha256(),
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EVP_sha384(), EVP_sha512(), EVP_mdc2(), EVP_ripemd160(), EVP_blake2b, and
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EVP_blake2s return B<EVP_MD> structures for the MD2, MD5, SHA1, SHA224, SHA256,
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SHA384, SHA512, MDC2, RIPEMD160, BLAKE2b, and BLAKE2s digest algorithms
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respectively.
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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.
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=head1 RETURN VALUES
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EVP_DigestInit_ex(), EVP_DigestUpdate() and EVP_DigestFinal_ex() return 1 for
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success and 0 for failure.
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EVP_MD_CTX_copy_ex() 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() and
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EVP_MD_CTX_block_size() return the digest or block size in bytes.
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EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha1(),
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EVP_mdc2(), EVP_ripemd160(), EVP_blake2b(), and EVP_blake2s() return pointers
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to the 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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New applications should use the SHA2 digest algorithms such as SHA256.
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The other digest algorithms are still in common use.
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For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
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set to NULL to use the default digest implementation.
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The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy() are
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obsolete but are retained to maintain compatibility with existing code. New
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applications should use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and
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EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest context
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instead of initializing and cleaning it up on each call and allow non default
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implementations of digests to be specified.
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If digest contexts are not cleaned up after use
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memory leaks will occur.
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EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(),
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EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as
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macros.
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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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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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mdctx = EVP_MD_CTX_new();
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EVP_DigestInit_ex(mdctx, md, NULL);
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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_ex(mdctx, md_value, &md_len);
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EVP_MD_CTX_free(mdctx);
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printf("Digest is: ");
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for(i = 0; i < md_len; i++)
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printf("%02x", md_value[i]);
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printf("\n");
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/* Call this once before exit. */
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EVP_cleanup();
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exit(0);
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}
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=head1 SEE ALSO
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L<dgst(1)>,
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L<evp(3)>
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=head1 HISTORY
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B<EVP_MD_CTX> became opaque in OpenSSL 1.1. Consequently, stack
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allocated B<EVP_MD_CTX>s are no longer supported.
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EVP_MD_CTX_create() and EVP_MD_CTX_destroy() were renamed to
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EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL 1.1.
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The link between digests and signing algorithms was fixed in OpenSSL 1.0 and
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later, so now EVP_sha1() can be used with RSA and DSA. The legacy EVP_dss1()
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was removed in OpenSSL 1.1.0
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=cut
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