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OPENSSL_ADD_ALL_ALGORITHMS(3) Library Functions Manual OPENSSL_ADD_ALL_ALGORITHMS(3)

OpenSSL_add_all_algorithms, OpenSSL_add_all_ciphers, OpenSSL_add_all_digests, EVP_cleanup
add algorithms to internal table

#include <openssl/evp.h>
void
OpenSSL_add_all_algorithms(void);
void
OpenSSL_add_all_ciphers(void);
void
OpenSSL_add_all_digests(void);
void
EVP_cleanup(void);

These functions are deprecated. It is never useful for any application program to call any of them explicitly. The library automatically calls them internally whenever needed.
OpenSSL keeps an internal table of digest algorithms and ciphers. It uses this table to look up ciphers via functions such as EVP_get_cipherbyname(3).
OpenSSL_add_all_algorithms() adds all algorithms to the table (digests and ciphers).
OpenSSL_add_all_digests() adds all digest algorithms to the table.
OpenSSL_add_all_ciphers() adds all encryption algorithms to the table including password based encryption algorithms.
If any of the above functions is called more than once, only the first call has an effect.
EVP_cleanup() removes all ciphers and digests from the table.

evp(3), EVP_DigestInit(3), EVP_EncryptInit(3), OPENSSL_config(3), OPENSSL_init_crypto(3)

EVP_cleanup() and precursor functions SSLeay_add_all_algorithms(), SSLeay_add_all_ciphers(), and SSLeay_add_all_digests() first appeared in SSLeay 0.8.0 and have been available since OpenBSD 2.4.
OpenSSL_add_all_algorithms(), OpenSSL_add_all_ciphers(), and OpenSSL_add_all_digests() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.

Although the functions do not return error codes, it is possible for them to fail. This will only happen as a result of a memory allocation failure so this is not too much of a problem in practice.
March 27, 2018 OpenBSD-current