BN_num_bytes(3)                     OpenSSL                    BN_num_bytes(3)



NNAAMMEE
       BN_num_bits, BN_num_bytes, BN_num_bits_word - get BIGNUM size

SSYYNNOOPPSSIISS
        #include <openssl/bn.h>

        int BN_num_bytes(const BIGNUM *a);

        int BN_num_bits(const BIGNUM *a);

        int BN_num_bits_word(BN_ULONG w);

DDEESSCCRRIIPPTTIIOONN
       _B_N___n_u_m___b_y_t_e_s_(_) returns the size of a BBIIGGNNUUMM in bytes.

       _B_N___n_u_m___b_i_t_s___w_o_r_d_(_) returns the number of significant bits in a word.
       If we take 0x00000432 as an example, it returns 11, not 16, not 32.
       Basically, except for a zero, it returns _f_l_o_o_r_(_l_o_g_2_(_w_)_)_+_1.

       _B_N___n_u_m___b_i_t_s_(_) returns the number of significant bits in a BBIIGGNNUUMM, fol-
       lowing the same principle as _B_N___n_u_m___b_i_t_s___w_o_r_d_(_).

       _B_N___n_u_m___b_y_t_e_s_(_) is a macro.

RREETTUURRNN VVAALLUUEESS
       The size.

NNOOTTEESS
       Some have tried using _B_N___n_u_m___b_i_t_s_(_) on individual numbers in RSA keys,
       DH keys and DSA keys, and found that they don't always come up with the
       number of bits they expected (something like 512, 1024, 2048, ...).
       This is because generating a number with some specific number of bits
       doesn't always set the highest bits, thereby making the number of _s_i_g_-
       _n_i_f_i_c_a_n_t bits a little lower.  If you want to know the "key size" of
       such a key, either use functions like _R_S_A___s_i_z_e_(_), _D_H___s_i_z_e_(_) and
       _D_S_A___s_i_z_e_(_), or use _B_N___n_u_m___b_y_t_e_s_(_) and multiply with 8 (although there's
       no real guarantee that will match the "key size", just a lot more prob-
       ability).

SSEEEE AALLSSOO
       _b_n(3), _D_H___s_i_z_e(3), _D_S_A___s_i_z_e(3), _R_S_A___s_i_z_e(3)

HHIISSTTOORRYY
       _B_N___n_u_m___b_y_t_e_s_(_), _B_N___n_u_m___b_i_t_s_(_) and _B_N___n_u_m___b_i_t_s___w_o_r_d_(_) are available in
       all versions of SSLeay and OpenSSL.



1.0.1u                            2016-09-22                   BN_num_bytes(3)