RSA_SECURITY_BITS(3)       Library Functions Manual       RSA_SECURITY_BITS(3)

NAME
     RSA_security_bits, DSA_security_bits, DH_security_bits, BN_security_bits
     - get security strength

SYNOPSIS
     #include <openssl/rsa.h>

     int
     RSA_security_bits(const RSA *rsa);

     #include <openssl/dsa.h>

     int
     DSA_security_bits(const DSA *dsa);

     #include <openssl/dh.h>

     int
     DH_security_bits(const DH *dh);

     #include <openssl/bn.h>

     int
     BN_security_bits(int pubbits, int privbits);

DESCRIPTION
     These functions return the security strength of some specific types of
     cryptographic keys, measured in bits.  It is approximately the binary
     logarithm of the number of operations an attacker has to perform in order
     to break the key.

     RSA_security_bits() uses only the number of significant bits in the
     public modulus of rsa as returned by RSA_bits(3).  It returns

           256    for    15360    or more significant bits
           192           7680
           128           3072
           112           2048
           80            1024

     or 0 otherwise.

     DSA_security_bits() uses the number of significant bits in the public
     domain parameter p contained in the dsa object, which is equal to the
     size of the public key, in the same way as RSA_security_bits().  In
     addition, the public domain parameter q contained in the dsa object,
     which is equal to the size of the private key, is inspected.  The return
     value is either the security strength according to the above table or
     half the size of the private key, whichever is smaller.  If the return
     value would be smaller than 80, 0 is returned instead.

     DH_security_bits() uses the number of significant bits in the shared
     secret contained in the dh object as returned by DH_bits(3) in the same
     way as RSA_security_bits().  If dh contains the domain parameter q, its
     number of significant bits is used in the same way as for
     DSA_security_bits() to limit the return value.  Otherwise, if dh contains
     the length of the secret exponent in bits, that number is used.  If
     neither is available, only the above table is used without calculating a
     minimum.

     BN_security_bits() is a combined function.  If -1 is passed for the
     privbits argument, it behaves like RSA_security_bits().  Otherwise, it
     behaves like DSA_security_bits().

RETURN VALUES
     All these functions return numbers in the range from 0 to 256 inclusive.

     DSA_security_bits() fails and returns -1 unless both of the p and q
     domain parameters are present.

SEE ALSO
     BN_num_bits(3), DH_bits(3), DH_get0_pqg(3), DSA_get0_pqg(3), RSA_bits(3),
     SSL_CTX_set_security_level(3)

     Elaine Barker, Recommendation for Key Management, U.S. National Institute
     of Standards and Technology, NIST Special Publication 800-57 Part 1
     Revision 5, https://doi.org/10.6028/NIST.SP.800-57pt1r5, Gaithersburg,
     MD, May 2020.

HISTORY
     These functions first appeared in OpenSSL 1.1.0 and have been available
     since OpenBSD 7.2.

Linux 6.8.2-arch2-1              July 13, 2022             Linux 6.8.2-arch2-1