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EEVVPP__SSeeaall_._._. and EEVVPP__OOppeenn_._._. provide public key encryption and decryption to implement digital "envelopes".
The EEVVPP__SSiiggnn_._._. and EEVVPP__VVeerriiffyy_._._. functions implement digital signatures.
Symmetric encryption is available with the EEVVPP__EEnnccrryypptt_._._. functions. The EEVVPP__DDiiggeesstt_._._. functions provide message digests.
The EEVVPP__PPKKEEYY_._._. functions provide a high level interface to asymmetric algorithms.
Algorithms are loaded with _O_p_e_n_S_S_L___a_d_d___a_l_l___a_l_g_o_r_i_t_h_m_s(3).
All the symmetric algorithms (ciphers), digests and asymmetric algorithms (public key algorithms) can be replaced by ENGINE modules providing alternative implementations. If ENGINE implementations of ciphers or digests are registered as defaults, then the various EVP functions will automatically use those implementations automatically in preference to built in software implementations. For more information, consult the _e_n_g_i_n_e(3) man page.
Although low level algorithm specific functions exist for many algorithms their use is discouraged. They cannot be used with an ENGINE and ENGINE versions of new algorithms cannot be accessed using the low level functions. Also makes code harder to adapt to new algorithms and some options are not cleanly supported at the low level and some operations are more efficient using the high level interface.