Sortix nightly manual
This manual documents Sortix nightly, a development build that has not been officially released. You can instead view this document in the latest official manual.
|BN_NUM_BYTES(3)||Library Functions Manual||BN_NUM_BYTES(3)|
get BIGNUM size
BN_num_bytes(const BIGNUM *a); int
BN_num_bits(const BIGNUM *a); int
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
floor(log2(w)) + 1.
BN_num_bits() returns the number of significant bits in a BIGNUM, following the same principle as
BN_num_bytes() is a macro. 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(3), DH_size(3), and 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 probability). BN_new(3), DH_size(3), DSA_size(3), RSA_size(3)
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||Debian|