- NAME
- SYNOPSIS
- DESCRIPTION
- PARAMETERS
- CONTROLS
- FLAGS
- RETURN VALUES
- NOTES
- EXAMPLES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

EVP_MD_fetch, EVP_MD_up_ref, EVP_MD_free, EVP_MD_get_params, EVP_MD_gettable_params, EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy, EVP_MD_CTX_copy_ex, EVP_MD_CTX_ctrl, EVP_MD_CTX_set_params, EVP_MD_CTX_get_params, EVP_MD_settable_ctx_params, EVP_MD_gettable_ctx_params, EVP_MD_CTX_settable_params, EVP_MD_CTX_gettable_params, EVP_MD_CTX_set_flags, EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags, EVP_Digest, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal, EVP_MD_is_a, EVP_MD_name, EVP_MD_number, EVP_MD_names_do_all, EVP_MD_provider, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags, EVP_MD_CTX_name, EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size, EVP_MD_CTX_md_data, EVP_MD_CTX_update_fn, EVP_MD_CTX_set_update_fn, EVP_md_null, EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj, EVP_MD_CTX_pkey_ctx, EVP_MD_CTX_set_pkey_ctx, EVP_MD_do_all_provided - EVP digest routines

# SYNOPSIS

     #include <openssl/evp.h>

     EVP_MD *EVP_MD_fetch(OPENSSL_CTX *ctx, const char *algorithm,
                          const char *properties);
     int EVP_MD_up_ref(EVP_MD *md);
     void EVP_MD_free(EVP_MD *md);
     int EVP_MD_get_params(const EVP_MD *digest, OSSL_PARAM params[]);
     const OSSL_PARAM *EVP_MD_gettable_params(const EVP_MD *digest);
     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_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
     int EVP_MD_CTX_get_params(EVP_MD_CTX *ctx, OSSL_PARAM params[]);
     int EVP_MD_CTX_set_params(EVP_MD_CTX *ctx, const OSSL_PARAM params[]);
     const OSSL_PARAM *EVP_MD_settable_ctx_params(const EVP_MD *md);
     const OSSL_PARAM *EVP_MD_gettable_ctx_params(const EVP_MD *md);
     const OSSL_PARAM *EVP_MD_CTX_settable_params(EVP_MD_CTX *ctx);
     const OSSL_PARAM *EVP_MD_CTX_gettable_params(EVP_MD_CTX *ctx);
     void EVP_MD_CTX_set_flags(EVP_MD_CTX *ctx, int flags);
     void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);
     int EVP_MD_CTX_test_flags(const EVP_MD_CTX *ctx, int flags);

     int EVP_Digest(const void *data, size_t count, unsigned char *md,
                    unsigned int *size, const EVP_MD *type, ENGINE *impl);
     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_DigestFinalXOF(EVP_MD_CTX *ctx, unsigned char *md, size_t len);

     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);

     const char *EVP_MD_name(const EVP_MD *md);
     int EVP_MD_number(const EVP_MD *md);
     int EVP_MD_is_a(const EVP_MD *md, const char *name);
     void EVP_MD_names_do_all(const EVP_MD *md,
                              void (*fn)(const char *name, void *data),
                              void *data);
     const OSSL_PROVIDER *EVP_MD_provider(const EVP_MD *md);
     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);
     unsigned long EVP_MD_flags(const EVP_MD *md);

     const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
     const char *EVP_MD_CTX_name(const EVP_MD_CTX *ctx);
     int EVP_MD_CTX_size(const EVP_MD_CTX *ctx);
     int EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);
     int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
     void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);
     int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,
                                                  const void *data, size_t count);
     void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
                                   int (*update)(EVP_MD_CTX *ctx,
                                                 const void *data, size_t count));

     const EVP_MD *EVP_md_null(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);

     EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);
     void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);

     void EVP_MD_do_all_provided(OPENSSL_CTX *libctx,
                                 void (*fn)(EVP_MD *mac, void *arg),
                                 void *arg);

# DESCRIPTION

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

The EVP_MD type is a structure for digest method implementation.

`EVP_MD_fetch()`

  Fetches the digest implementation for the given algorithm from any provider offering it, within the criteria given by the properties. See provider(7)/Fetching algorithms for further information.

  The returned value must eventually be freed with `EVP_MD_free()`.

  Fetched EVP_MD structures are reference counted.

`EVP_MD_up_ref()`

  Increments the reference count for an EVP_MD structure.

`EVP_MD_free()`

  Decrements the reference count for the fetched EVP_MD structure. If the reference count drops to 0 then the structure is freed.

`EVP_MD_CTX_new()`

  Allocates and returns a digest context.

`EVP_MD_CTX_reset()`

  Resets the digest context ctx. This can be used to reuse an already existing context.

`EVP_MD_CTX_free()`

  Cleans up digest context ctx and frees up the space allocated to it.

`EVP_MD_CTX_ctrl()`

  This is a legacy method. `EVP_MD_CTX_set_params()` and `EVP_MD_CTX_get_params()` is the mechanism that should be used to set and get parameters that are used by providers. Performs digest-specific control actions on context ctx. The control command is indicated in cmd and any additional arguments in p1 and p2. `EVP_MD_CTX_ctrl()` must be called after `EVP_DigestInit_ex()`. Other restrictions may apply depending on the control type and digest implementation. See CONTROLS below for more information.

`EVP_MD_get_params()`

  Retrieves the requested list of params from a MD md. See PARAMETERS below for more information.

`EVP_MD_CTX_get_params()`

  Retrieves the requested list of params from a MD context ctx. See PARAMETERS below for more information.

`EVP_MD_CTX_set_params()`

  Sets the list of params into a MD context ctx. See PARAMETERS below for more information.

`EVP_MD_gettable_params()`, `EVP_MD_gettable_ctx_params()`, `EVP_MD_settable_ctx_params()`, `EVP_MD_CTX_gettable_params()`, `EVP_MD_CTX_settable_params()`

  Get a OSSL_PARAM array that describes the retrievable and settable parameters. `EVP_MD_gettable_params()` returns parameters that can be used with `EVP_MD_get_params()`. `EVP_MD_gettable_ctx_params()` and `EVP_MD_CTX_gettable_params()` return parameters that can be used with `EVP_MD_CTX_get_params()`. `EVP_MD_settable_ctx_params()` and `EVP_MD_CTX_settable_params()` return parameters that can be used with `EVP_MD_CTX_set_params()`. See OSSL_PARAM(3) for the use of OSSL_PARAM as parameter descriptor.

`EVP_MD_CTX_set_flags()`, `EVP_MD_CTX_clear_flags()`, `EVP_MD_CTX_test_flags()`

  Sets, clears and tests ctx flags. See FLAGS below for more information.

`EVP_Digest()`

  A wrapper around the Digest Init_ex, Update and Final_ex functions. Hashes count bytes of data at data using a digest type from ENGINE impl. The digest value is placed in md and its length is written at size if the pointer is not NULL. At most EVP_MAX_MD_SIZE bytes will be written. If impl is NULL the default implementation of digest type is used.

`EVP_DigestInit_ex()`

  Sets up digest context ctx to use a digest type. type is typically supplied by a function such as EVP_sha1(), or a value explicitly fetched with `EVP_MD_fetch()`.

  If impl is non-NULL, its implementation of the digest type is used if there is one, and if not, the default implementation is used.

`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_DigestFinalXOF()`

  Interfaces to extendable-output functions, XOFs, such as SHAKE128 and SHAKE256. It retrieves the digest value from ctx and places it in len-sized <B>md. After calling this function no additional calls to `EVP_DigestUpdate()` can be made, but `EVP_DigestInit_ex()` can be called to initialize a new 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.

`EVP_DigestInit()`

  Behaves in the same way as `EVP_DigestInit_ex()` except it always uses the default digest implementation and calls `EVP_MD_CTX_reset()`.

`EVP_DigestFinal()`

  Similar to `EVP_DigestFinal_ex()` except the digest context ctx is automatically cleaned up.

`EVP_MD_CTX_copy()`

  Similar to `EVP_MD_CTX_copy_ex()` except the destination out does not have to be initialized.

`EVP_MD_is_a()`

  Returns 1 if md is an implementation of an algorithm that's identifiable with name, otherwise 0.

  If md is a legacy digest (it's the return value from the likes of EVP_sha256() rather than the result of an EVP_MD_fetch()), only cipher names registered with the default library context (see OPENSSL_CTX(3)) will be considered.

`EVP_MD_number()`

  Returns the internal dynamic number assigned to the md. This is only useful with fetched EVP_MDs.

`EVP_MD_name()`, `EVP_MD_CTX_name()`

  Return the name of the given message digest. For fetched message digests with multiple names, only one of them is returned; it's recommended to use `EVP_MD_names_do_all()` instead.

`EVP_MD_names_do_all()`

  Traverses all names for the md, and calls fn with each name and data. This is only useful with fetched EVP_MDs.

`EVP_MD_provider()`

  Returns an OSSL_PROVIDER pointer to the provider that implements the given EVP_MD.

`EVP_MD_size()`, `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()`, `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()`, `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 ASN1 OIDs.

`EVP_MD_CTX_md_data()`

  Return the digest method private data for the passed EVP_MD_CTX. The space is allocated by OpenSSL and has the size originally set with `EVP_MD_meth_set_app_datasize()`.

`EVP_MD_CTX_md()`

  Returns the EVP_MD structure corresponding to the passed EVP_MD_CTX. This will be the same EVP_MD object originally passed to `EVP_DigestInit_ex()` (or other similar function) when the EVP_MD_CTX was first initialised. Note that where explicit fetch is in use (see EVP_MD_fetch(3)) the value returned from this function will not have its reference count incremented and therefore it should not be used after the EVP_MD_CTX is freed.

`EVP_MD_CTX_set_update_fn()`

  Sets the update function for ctx to update. This is the function that is called by EVP_DigestUpdate. If not set, the update function from the EVP_MD type specified at initialization is used.

`EVP_MD_CTX_update_fn()`

  Returns the update function for ctx.

`EVP_MD_flags()`

  Returns the md flags. Note that these are different from the EVP_MD_CTX ones. See EVP_MD_meth_set_flags(3) for more information.

`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_md_null()`

  A "null" message digest that does nothing: i.e. the hash it returns is of zero length.

`EVP_get_digestbyname()`, `EVP_get_digestbynid()`, `EVP_get_digestbyobj()`

  Returns an EVP_MD structure when passed a digest name, a digest NID or an ASN1_OBJECT structure respectively.

`EVP_MD_CTX_pkey_ctx()`

  Returns the EVP_PKEY_CTX assigned to ctx. The returned pointer should not be freed by the caller.

`EVP_MD_CTX_set_pkey_ctx()`

  Assigns an EVP_PKEY_CTX to EVP_MD_CTX. This is usually used to provide a customized EVP_PKEY_CTX to EVP_DigestSignInit(3) or EVP_DigestVerifyInit(3). The pctx passed to this function should be freed by the caller. A NULL pctx pointer is also allowed to clear the EVP_PKEY_CTX assigned to ctx. In such case, freeing the cleared EVP_PKEY_CTX or not depends on how the EVP_PKEY_CTX is created.

`EVP_MD_do_all_provided()`

  Traverses all messages digests implemented by all activated providers in the given library context libctx, and for each of the implementations, calls the given function fn with the implementation method and the given arg as argument.

# PARAMETERS

See OSSL_PARAM(3) for information about passing parameters.

`EVP_MD_CTX_set_params()` can be used with the following OSSL_PARAM keys:

"xoflen" (OSSL_PARAM_DIGEST_KEY_XOFLEN) <unsigned integer>

  Sets the digest length for extendable output functions. It is used by the SHAKE algorithm and should not exceed what can be given using a size_t.

"pad_type" (OSSL_PARAM_DIGEST_KEY_PAD_TYPE) <integer>

  Sets the pad type. It is used by the MDC2 algorithm.

`EVP_MD_CTX_get_params()` can be used with the following OSSL_PARAM keys:

"micalg" (OSSL_PARAM_DIGEST_KEY_MICALG) <UTF8 string>.

  Gets the digest Message Integrity Check algorithm string. This is used when creating S/MIME multipart/signed messages, as specified in RFC 3851. It may be used by external engines or providers.

# CONTROLS

`EVP_MD_CTX_ctrl()` can be used to send the following standard controls:

EVP_MD_CTRL_MICALG

  Gets the digest Message Integrity Check algorithm string. This is used when creating S/MIME multipart/signed messages, as specified in RFC 3851. The string value is written to p2.

EVP_MD_CTRL_XOF_LEN

  This control sets the digest length for extendable output functions to p1. Sending this control directly should not be necessary, the use of `EVP_DigestFinalXOF()` is preferred. Currently used by SHAKE.

# FLAGS

`EVP_MD_CTX_set_flags()`, `EVP_MD_CTX_clear_flags()` and `EVP_MD_CTX_test_flags()` can be used the manipulate and test these EVP_MD_CTX flags:

EVP_MD_CTX_FLAG_ONESHOT

  This flag instructs the digest to optimize for one update only, if possible.

EVP_MD_CTX_FLAG_NO_INIT

  This flag instructs `EVP_DigestInit()` and similar not to initialise the implementation specific data.

EVP_MD_CTX_FLAG_FINALISE

  Some functions such as EVP_DigestSign only finalise copies of internal contexts so additional data can be included after the finalisation call. This is inefficient if this functionality is not required, and can be disabled with this flag.

# RETURN VALUES

`EVP_MD_fetch()`

  Returns a pointer to a EVP_MD for success or NULL for failure.

`EVP_MD_up_ref()`

  Returns 1 for success or 0 for failure.

`EVP_DigestInit_ex()`, `EVP_DigestUpdate()`, `EVP_DigestFinal_ex()`

  Returns 1 for success and 0 for failure.

`EVP_MD_CTX_ctrl()`

  Returns 1 if successful or 0 for failure.

`EVP_MD_CTX_set_params()`, `EVP_MD_CTX_get_params()`

  Returns 1 if successful or 0 for failure.

`EVP_MD_CTX_settable_params()`, `EVP_MD_CTX_gettable_params()`

  Return an array of constant OSSL_PARAMs, or NULL if there is none to get.

`EVP_MD_CTX_copy_ex()`

  Returns 1 if successful or 0 for failure.

`EVP_MD_type()`, `EVP_MD_pkey_type()`

  Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none exists.

`EVP_MD_size()`, `EVP_MD_block_size()`, `EVP_MD_CTX_size()`, `EVP_MD_CTX_block_size()`

  Returns the digest or block size in bytes.

`EVP_md_null()`

  Returns a pointer to the EVP_MD structure of the "null" message digest.

`EVP_get_digestbyname()`, `EVP_get_digestbynid()`, `EVP_get_digestbyobj()`

  Returns either an EVP_MD structure or NULL if an error occurs.

`EVP_MD_CTX_set_pkey_ctx()`

  This function has no return value.

# NOTES

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 SHA-2 (such as EVP_sha256(3)) or the SHA-3 digest algorithms (such as EVP_sha3_512(3)). 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.

`EVP_MD_CTX_name()`, `EVP_MD_CTX_size()`, `EVP_MD_CTX_block_size()`, `EVP_MD_CTX_type()`, `EVP_get_digestbynid()` and `EVP_get_digestbyobj()` are defined as macros.

`EVP_MD_CTX_ctrl()` sends commands to message digests for additional configuration or control.

# 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 <string.h>
     #include <openssl/evp.h>

     int main(int argc, char *argv[])
     {
         EVP_MD_CTX *mdctx;
         const EVP_MD *md;
         char mess1[] = "Test Message\n";
         char mess2[] = "Hello World\n";
         unsigned char md_value[EVP_MAX_MD_SIZE];
         unsigned int md_len, i;

         if (argv[1] == NULL) {
             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");

         exit(0);
     }

# SEE ALSO

EVP_MD_meth_new(3), openssl-dgst(1), evp(7), OSSL_PROVIDER(3), OSSL_PARAM(3)

The full list of digest algorithms are provided below.

EVP_blake2b512(3), EVP_md2(3), EVP_md4(3), EVP_md5(3), EVP_mdc2(3), EVP_ripemd160(3), EVP_sha1(3), EVP_sha224(3), EVP_sha3_224(3), EVP_sm3(3), EVP_whirlpool(3) provider(7)/Fetching algorithms

# HISTORY

The `EVP_MD_CTX_create()` and `EVP_MD_CTX_destroy()` functions were renamed to `EVP_MD_CTX_new()` and `EVP_MD_CTX_free()` in OpenSSL 1.1.0, respectively.

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.

The EVP_dss1() function was removed in OpenSSL 1.1.0.

The `EVP_MD_CTX_set_pkey_ctx()` function was added in 1.1.1.

The `EVP_MD_fetch()`, `EVP_MD_free()`, `EVP_MD_up_ref()`, `EVP_MD_CTX_set_params()` and `EVP_MD_CTX_get_params()` functions were added in 3.0.

# COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.