=pod =head1 NAME EVP_MD_fetch, EVP_CIPHER_fetch - Functions to explicitly fetch algorithm implementations =head1 SYNOPSIS #include EVP_MD *EVP_MD_fetch(OPENSSL_CTX *ctx, const char *algorithm, const char *properties); EVP_CIPHER *EVP_CIPHER_fetch(OPENSSL_CTX *ctx, const char *algorithm, const char *properties); =head1 DESCRIPTION Cryptographic algorithms are represented by different OpenSSL objects depending on what type of algorithm it is. The following cryptographic algorithm types are supported. =over 4 =item B Represents a digest algorithm. =item B Represents a symmetric cipher algorithm. =item B Represents a Message Authentication Code algorithm. =item B Represents a Key Derivation Function algorithm. =back The algorithm objects may or may not have an associated algorithm implementation. Cryptographic algorithms are implemented by providers. Any algorithm may be supported by zero or more providers. In order to use an algorithm an implementation must first be obtained. This can happen in one of three ways, i.e. implicit fetch, explicit fetch or user defined. =over 4 =item Implicit Fetch With implicit fetch an application can use functions such as L, L or L to obtain an algorithm object with no associated implementation. When used in a function like L or L the actual implementation to be used will be fetched implicitly using default search criteria. Typically, this will return an implementation of the appropriate algorithm from the default provider unless the default search criteria have been changed and/or different providers have been loaded. =item Explicit Fetch With explicit fetch an application uses one of the "fetch" functions to obtain an algorithm object with an associated implementation. An implementation with the given name that satisfies the search criteria specified in the B parameter combined with the default search criteria will be looked for within the available providers and returned. See L for information on default search criteria and L for information about providers. =item User defined Using the user defined approach an application constructs its own algorithm object. See L and L for details. =back Having obtained an algorithm implementation as an algorithm object it can then be used to perform cryptographic operations. For example to calculate the digest of input data with an B algorithm object you can use functions such as L, L and L. The fetch functions will look for an algorithm within the providers that have been loaded into the B given in the B parameter. This parameter may be NULL in which case the default B will be used. See L and L for further details. The B parameter gives the name of the algorithm to be looked up. Different algorithms can be made available by loading different providers. The built-in default provider digest algorithm implementation names are: SHA1, SHA224, SHA256, SHA384, SHA512, SHA512-224, SHA512-256, SHA3-224, SHA3-256, SHA3-384, SHA3-512, SHAKE128, SHAKE256, SM3, BLAKE2b512, BLAKE2s256 and MD5-SHA1. The built-in default provider cipher algorithm implementation names are: AES-256-ECB, AES-192-ECB, AES-128-ECB, AES-256-CBC, AES-192-CBC, AES-128-CBC, AES-256-OFB, AES-192-OFB, AES-128-OFB, AES-256-CFB, AES-192-CFB, AES-128-CFB, AES-256-CFB1, AES-192-CFB1, AES-128-CFB1, AES-256-CFB8, AES-192-CFB8, AES-128-CFB8, AES-256-CTR, AES-192-CTR, AES-128-CTR, id-aes256-GCM, id-aes192-GCM and id-aes128-GCM. Additional algorithm implementations may be obtained by loading the "legacy" provider. The legacy provider digest algorithms are: RIPEMD160, MD2, MD4, MD5, MDC2 and whirlpool. The B parameter specifies the search criteria that will be used to look for an algorithm implementation. Properties are given as a comma delimited string of name value pairs. In order for an implementation to match, all the properties in the query string must match those defined for that implementation. Any properties defined by an implementation but not given in the query string are ignored. All algorithm implementations in the default provider have the property "default=yes". All algorithm implementations in the legacy provider have the property "legacy=yes". All algorithm implementations in the FIPS provider have the property "fips=yes". In the event that more than one implementation of the given algorithm name matches the specified properties then an unspecified one of those implementations may be returned. The B parameter may be NULL in which case any implementation from the available providers with the given algorithm name will be returned. The return value from a call to EVP_MD_fetch() must be freed by the caller using L. Note that EVP_MD objects are reference counted. See L. The return value from a call to EVP_CIPHER_fetch() must be freed by the caller using L. Note that EVP_CIPHER objects are reference counted. See L. =head1 NOTES Where an application that previously used implicit fetch is converted to use explicit fetch care should be taken with the L function. Specifically, this function returns the EVP_MD object orginally passed to EVP_DigestInit_ex() (or other similar function). With implicit fetch the returned EVP_MD object is guaranteed to be available throughout the application lifetime. However, with explicit fetch EVP_MD objects are reference counted. EVP_MD_CTX_md does not increment the reference count and so the returned EVP_MD object may not be accessible beyond the lifetime of the EVP_MD_CTX it is associated with. =head1 RETURN VALUES EVP_MD_fetch() returns a pointer to the algorithm implementation represented by an EVP_MD object, or NULL on error. =head1 EXAMPLES Fetch any available implementation of SHA256 in the default context: EVP_MD *md = EVP_MD_fetch(NULL, "SHA256", NULL); ... EVP_MD_meth_free(md); Fetch any available implementation of AES-128-CBC in the default context: EVP_CIPHER *cipher = EVP_CIPHER_fetch(NULL, "AES-128-CBC", NULL); ... EVP_CIPHER_meth_free(cipher); Fetch an implementation of SHA256 from the default provider in the default context: EVP_MD *md = EVP_MD_fetch(NULL, "SHA256", "default=yes"); ... EVP_MD_meth_free(md); Fetch an implementation of SHA256 that is not from the default provider in the default context: EVP_MD *md = EVP_MD_fetch(NULL, "SHA256", "default=no"); ... EVP_MD_meth_free(md); Fetch an implementation of SHA256 from the default provider in the specified context: EVP_MD *md = EVP_MD_fetch(ctx, "SHA256", "default=yes"); ... EVP_MD_meth_free(md); Load the legacy provider into the default context and then fetch an implementation of whirlpool from it: /* This only needs to be done once - usually at application start up */ OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy"); EVP_MD *md = EVP_MD_fetch(NULL, "whirlpool", "legacy=yes"); ... EVP_MD_meth_free(md); Note that in the above example the property string "legacy=yes" is optional since, assuming no other providers have been loaded, the only implmentation of the "whirlpool" algorithm is in the "legacy" provider. Also note that the default provider should be explicitly loaded if it is required in addition to other providers: /* This only needs to be done once - usually at application start up */ OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy"); OSSL_PROVIDER *default = OSSL_PROVIDER_load(NULL, "default"); EVP_MD *md_whirlpool = EVP_MD_fetch(NULL, "whirlpool", NULL); EVP_MD *md_sha256 = EVP_MD_fetch(NULL, "SHA256", NULL); ... EVP_MD_meth_free(md_whirlpool); EVP_MD_meth_free(md_sha256); =head1 SEE ALSO L, L, L, L, L, L, L, L, L, L, L =head1 HISTORY The functions described here were added in OpenSSL 3.0. =head1 COPYRIGHT Copyright 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 L. =cut