EVP_DIGESTINIT(3)

NAME
EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_MD_CTX_cleanup, EVP_MD_CTX_destroy, EVP_MD_CTX_ctrl, EVP_DigestInit_ex, EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_MD_CTX_copy_ex, EVP_DigestInit, EVP_DigestFinal, EVP_MD_CTX_copy, EVP_MAX_MD_SIZE, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size, EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null, EVP_md5, EVP_md5_sha1, EVP_sha1, EVP_sha224, EVP_sha256, EVP_sha384, EVP_sha512, EVP_dss, EVP_dss1, EVP_ripemd160, EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj - EVP digest routines

SYNOPSIS
#include <openssl/evp.h>
EVP_MD_CTX *
EVP_MD_CTX_new(void);
int
EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
void
EVP_MD_CTX_free(EVP_MD_CTX *ctx);
void
EVP_MD_CTX_init(EVP_MD_CTX *ctx);
EVP_MD_CTX *
EVP_MD_CTX_create(void);
int
EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
void
EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
int
EVP_MD_CTX_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
int
EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
int
EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
int
EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
int
EVP_MD_CTX_copy_ex(EVP_MD_CTX *out, const EVP_MD_CTX *in);
int
EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
int
EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
int
EVP_MD_CTX_copy(EVP_MD_CTX *out, EVP_MD_CTX *in);
#define EVP_MAX_MD_SIZE 64 /* SHA512 */
int
EVP_MD_type(const EVP_MD *md);
int
EVP_MD_pkey_type(const EVP_MD *md);
int
EVP_MD_size(const EVP_MD *md);
int
EVP_MD_block_size(const EVP_MD *md);
const EVP_MD *
EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
int
EVP_MD_CTX_size(const EVP_MD *ctx);
int
EVP_MD_CTX_block_size(const EVP_MD *ctx);
int
EVP_MD_CTX_type(const EVP_MD *ctx);
const EVP_MD *
EVP_md_null(void);
const EVP_MD *
EVP_md5(void);
const EVP_MD *
EVP_md5_sha1(void);
const EVP_MD *
EVP_sha1(void);
const EVP_MD *
EVP_sha224(void);
const EVP_MD *
EVP_sha256(void);
const EVP_MD *
EVP_sha384(void);
const EVP_MD *
EVP_sha512(void);
const EVP_MD *
EVP_dss(void);
const EVP_MD *
EVP_dss1(void);
const EVP_MD *
EVP_ripemd160(void);
const EVP_MD *
EVP_get_digestbyname(const char *name);
const EVP_MD *
EVP_get_digestbynid(int type);
const EVP_MD *
EVP_get_digestbyobj(const ASN1_OBJECT *o);

DESCRIPTION
The EVP digest routines are a high level interface to message digests and should be used instead of the cipher-specific functions.

EVP_MD_CTX_new() allocates a new, empty digest context.

EVP_MD_CTX_reset() cleans up ctx and resets it to the state it had after EVP_MD_CTX_new(), such that it can be reused. It is also suitable for digest contexts on the stack that were used and are no longer needed.

EVP_MD_CTX_free() cleans up ctx and frees the space allocated to it.

EVP_MD_CTX_init() is a deprecated function to clear a digest context on the stack before use. Do not use it on a digest context returned from EVP_MD_CTX_new() or one one that was already used.

EVP_MD_CTX_create(), EVP_MD_CTX_cleanup(), and EVP_MD_CTX_destroy() are deprecated aliases for EVP_MD_CTX_new(), EVP_MD_CTX_reset(), and EVP_MD_CTX_free(), respectively.

EVP_MD_CTX_ctrl() performs digest-specific control actions on the context ctx.

EVP_DigestInit_ex() sets up the digest context ctx to use a digest type from ENGINE impl. The type will typically be supplied by a function such as EVP_sha1(). If impl is NULL, then the default implementation of digest type is used. If ctx points to an unused object on the stack, it must be initialized with EVP_MD_CTX_init() before calling this function.

EVP_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.

EVP_DigestFinal_ex() retrieves the digest value from ctx and places it in md. If the s parameter is not NULL, 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 EVP_MAX_MD_SIZE 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.

EVP_MD_CTX_copy_ex() can be used to copy the message digest state from in to out. This is useful if large amounts of data are to be hashed which only differ in the last few bytes. If out points to an unused object on the stack, it must be initialized with EVP_MD_CTX_init() before calling this function.

EVP_DigestInit() is a deprecated function behaving like EVP_DigestInit_ex() except that it always uses the default digest implementation and that it requires EVP_MD_CTX_reset() before it can be used on a context that was already used.

EVP_DigestFinal() is a deprecated function behaving like EVP_DigestFinal_ex() except that the digest context ctx is automatically cleaned up after use by calling EVP_MD_CTX_reset() internally.

EVP_MD_CTX_copy() is a deprecated function behaving like EVP_MD_CTX_copy_ex() except that it requires EVP_MD_CTX_reset() before a context that was already used can be passed as out.

EVP_MD_size() and EVP_MD_CTX_size() return the size of the message digest when passed an EVP_MD or an EVP_MD_CTX structure, i.e. the size of the hash.

EVP_MD_block_size() and EVP_MD_CTX_block_size() return the block size of the message digest when passed an EVP_MD or an EVP_MD_CTX structure.

EVP_MD_type() and EVP_MD_CTX_type() return the NID of the OBJECT IDENTIFIER representing the given message digest when passed an EVP_MD structure. For example EVP_MD_type(EVP_sha1()) returns NID_sha1. This function is normally used when setting ASN.1 OIDs.

EVP_MD_pkey_type() returns the NID of the public key signing algorithm associated with this digest. For example EVP_sha1() is associated with RSA so this will return NID_sha1WithRSAEncryption. Since digests and signature algorithms are no longer linked this function is only retained for compatibility reasons.

EVP_md5(), EVP_sha1(), EVP_sha224(), EVP_sha256(), EVP_sha384(), EVP_sha512(), and EVP_ripemd160() return EVP_MD structures for the MD5, SHA1, SHA224, SHA256, SHA384, SHA512 and RIPEMD160 digest algorithms respectively.

EVP_md5_sha1() returns an EVP_MD structure that provides concatenated MD5 and SHA1 message digests.

EVP_dss() and EVP_dss1() return EVP_MD structures for SHA1 digest algorithms but using DSS (DSA) 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.

EVP_md_null() is a "null" message digest that does nothing: i.e. the hash it returns is of zero length.

EVP_get_digestbyname(), EVP_get_digestbynid(), and EVP_get_digestbyobj() return an EVP_MD structure when passed a digest name, a digest NID, or an ASN1_OBJECT structure respectively. The digest table must be initialized using, for example, OpenSSL_add_all_digests(3) for these functions to work.

EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(), EVP_get_digestbynid(), and EVP_get_digestbyobj() are implemented as macros.

The EVP 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.

New applications should use the SHA2 digest algorithms such as SHA256. The other digest algorithms are still in common use.

For most applications the impl parameter to EVP_DigestInit_ex() will be set to NULL 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 EVP_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.

If digest contexts are not cleaned up after use, memory leaks will occur.

RETURN VALUES
EVP_MD_CTX_new() and EVP_MD_CTX_create() return the new EVP_MD_CTX object or NULL for failure.

EVP_MD_CTX_reset() and EVP_MD_CTX_cleanup() always return 1.

EVP_MD_CTX_ctrl(), EVP_DigestInit_ex(), EVP_DigestUpdate(), EVP_DigestFinal_ex(), EVP_MD_CTX_copy_ex(), EVP_DigestInit(), EVP_DigestFinal(), and EVP_MD_CTX_copy() return 1 for success or 0 for failure.

EVP_MD_type(), EVP_MD_pkey_type(), and EVP_MD_CTX_type() return the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none exists.

EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(), and EVP_MD_CTX_block_size() return the digest or block size in bytes.

EVP_MD_CTX_md() returns the EVP_MD object used by ctx, or NULL if ctx is NULL.

EVP_md_null(), EVP_md5(), EVP_md5_sha1(), EVP_sha1(), EVP_dss(), EVP_dss1(), and EVP_ripemd160() return pointers to the corresponding EVP_MD structures.

EVP_get_digestbyname(), EVP_get_digestbynid(), and EVP_get_digestbyobj() return either an EVP_MD structure or NULL if an error occurs.

EXAMPLES
This example digests the data "Test Message\n" and "Hello World\n", using the digest name passed on the command line.

    #include <stdio.h>
    #include <openssl/evp.h>
    int
    main(int argc, char *argv[])
    {
    	EVP_MD_CTX *mdctx;
    	const EVP_MD *md;
    	const char mess1[] = "Test Message\n";
    	const char mess2[] = "Hello World\n";
    	unsigned char md_value[EVP_MAX_MD_SIZE];
    	int md_len, i;
    	OpenSSL_add_all_digests();
    	if (argc <= 1) {
    		printf("Usage: mdtest digestname\n");
    		exit(1);
    	}
    	md = EVP_get_digestbyname(argv[1]);
    	if (md == NULL) {
    		printf("Unknown message digest %s\n", argv[1]);
    		exit(1);
    	}
    	mdctx = EVP_MD_CTX_new();
    	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_free(mdctx);
    	printf("Digest is: ");
    	for(i = 0; i < md_len; i++)
    		printf("%02x", md_value[i]);
    	printf("\n");
    	return 0;
    }

SEE ALSO
evp(3)

HISTORY
EVP_DigestInit(), EVP_DigestUpdate(), EVP_DigestFinal(), EVP_MAX_MD_SIZE, EVP_MD_type(), EVP_MD_pkey_type(), EVP_MD_size(), EVP_MD_CTX_size(), EVP_MD_CTX_type(), EVP_md_null(), EVP_md5(), EVP_sha1(), EVP_dss(), EVP_dss1(), EVP_get_digestbyname(), EVP_get_digestbynid(), and EVP_get_digestbyobj() appeared in SSLeay 0.8.1b or earlier. EVP_MD_block_size(), EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_rc4_40(), EVP_rc2_40_cbc(), and EVP_ripemd160() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.

EVP_MD_CTX_copy() first appeared in OpenSSL 0.9.2b and has been available since OpenBSD 2.6.

EVP_MD_CTX_md() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7.

EVP_MD_CTX_init(), EVP_MD_CTX_create(), EVP_MD_CTX_cleanup(), EVP_MD_CTX_destroy(), EVP_DigestInit_ex(), EVP_DigestFinal_ex(), and EVP_MD_CTX_copy_ex() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.

EVP_sha224(), EVP_sha256(), EVP_sha384(), and EVP_sha512() first appeared in OpenSSL 0.8.7h and have been available since OpenBSD 4.0.

EVP_MD_CTX_ctrl() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 5.7.

EVP_MD_CTX_new(), EVP_MD_CTX_reset(), EVP_MD_CTX_free(), and EVP_md5_sha1() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 6.3.

The link between digests and signing algorithms was fixed in OpenSSL 1.0 and later, so now EVP_sha1() can be used with RSA and DSA; there is no need to use EVP_dss1() any more.