EVP_BytesToKey(3) OpenSSL EVP_BytesToKey(3) NNAAMMEE EVP_BytesToKey - password based encryption routine SSYYNNOOPPSSIISS #include int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md, const unsigned char *salt, const unsigned char *data, int datal, int count, unsigned char *key,unsigned char *iv); DDEESSCCRRIIPPTTIIOONN _E_V_P___B_y_t_e_s_T_o_K_e_y_(_) derives a key and IV from various parameters. ttyyppee is the cipher to derive the key and IV for. mmdd is the message digest to use. The ssaalltt parameter is used as a salt in the derivation: it should point to an 8 byte buffer or NULL if no salt is used. ddaattaa is a buffer containing ddaattaall bytes which is used to derive the keying data. ccoouunntt is the iteration count to use. The derived key and IV will be written to kkeeyy and iivv respectively. NNOOTTEESS A typical application of this function is to derive keying material for an encryption algorithm from a password in the ddaattaa parameter. Increasing the ccoouunntt parameter slows down the algorithm which makes it harder for an attacker to peform a brute force attack using a large number of candidate passwords. If the total key and IV length is less than the digest length and MMDD55 is used then the derivation algorithm is compatible with PKCS#5 v1.5 otherwise a non standard extension is used to derive the extra data. Newer applications should use a more modern algorithm such as PBKDF2 as defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC. KKEEYY DDEERRIIVVAATTIIOONN AALLGGOORRIITTHHMM The key and IV is derived by concatenating D_1, D_2, etc until enough data is available for the key and IV. D_i is defined as: D_i = HASH^count(D_(i-1) || data || salt) where || denotes concatentaion, D_0 is empty, HASH is the digest algo- rithm in use, HASH^1(data) is simply HASH(data), HASH^2(data) is HASH(HASH(data)) and so on. The initial bytes are used for the key and the subsequent bytes for the IV. RREETTUURRNN VVAALLUUEESS If ddaattaa is NULL, then _E_V_P___B_y_t_e_s_T_o_K_e_y_(_) returns the number of bytes needed to store the derived key. Otherwise, _E_V_P___B_y_t_e_s_T_o_K_e_y_(_) returns the size of the derived key in bytes, or 0 on error. SSEEEE AALLSSOO _e_v_p(3), _r_a_n_d(3), _E_V_P___E_n_c_r_y_p_t_I_n_i_t(3) HHIISSTTOORRYY 1.0.2u 2019-12-20 EVP_BytesToKey(3)