|BN_NUM_BYTES(3)||Library Functions Manual||BN_NUM_BYTES(3)|
BN_num_bytes() returns the size of a BIGNUM in bytes.
BN_num_bits_word() returns the number of
significant bits in a word. As an example, 0x00000432 returns 11, not 16 or
32. Basically, except for a zero, it returns
BN_num_bits() returns the number of
significant bits in a BIGNUM, following the same principle
BN_num_bytes() is a macro.
Some have tried using
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
DSA_size(3), 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
BN_num_bits() first appeared in SSLeay 0.5.1.
BN_num_bits_word() first appeared in SSLeay 0.5.2. These functions have been available since OpenBSD 2.4.
|March 27, 2018||OpenBSD-current|