Manual Pages for UNIX Operating System command usage for man BN_num_bits_word

OpenSSL                                    BN_num_bytes(3openssl)



NNNNAAAAMMMMEEEE
     BN_num_bits, BN_num_bytes, BN_num_bits_word - get BIGNUM
     size

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
      #include 

      int BN_num_bytes(const BIGNUM *a);

      int BN_num_bits(const BIGNUM *a);

      int BN_num_bits_word(BN_ULONG w);


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     BN_num_bytes() returns the size of a BBBBIIIIGGGGNNNNUUUUMMMM in bytes.

     BN_num_bits_word() 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
     floor(log2(w))+1.

     BN_num_bits() returns the number of significant bits in a
     BBBBIIIIGGGGNNNNUUUUMMMM, following the same principle as BN_num_bits_word().

     BN_num_bytes() is a macro.

RRRREEEETTTTUUUURRRRNNNN VVVVAAAALLLLUUUUEEEESSSS
     The size.

NNNNOOOOTTTTEEEESSSS
     Some have tried using BN_num_bits() 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 significant bits a little lower.  If you want to
     know the "key size" of such a key, either use functions like
     RSA_size(), DH_size() and DSA_size(), or use BN_num_bytes()
     and multiply with 8 (although there's no real guarantee that
     will match the "key size", just a lot more probability).

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     bn(3), DH_size(3), DSA_size(3), RSA_size(3)

HHHHIIIISSSSTTTTOOOORRRRYYYY
     BN_num_bytes(), BN_num_bits() and BN_num_bits_word() are
     available in all versions of SSLeay and OpenSSL.






1/Jul/2004             Last change: 0.9.8o                      1






OpenSSL                                    BN_num_bytes(3openssl)























































1/Jul/2004             Last change: 0.9.8o                      2