Switch the DRBGs from AES-128-CTR to AES-256-CTR

/*

 * Default security strength (in the sense of [NIST SP 800-90Ar1])

 * of the default OpenSSL DRBG, and the corresponding NID.

 *

 * Currently supported values: 128, 192, 256

 * NIST SP 800-90Ar1 supports the strength of the DRBG being smaller than that

 * of the cipher by collecting less entropy. The current DRBG implemantion does

 * not take RAND_DRBG_STRENGTH into account and sets the strength of the DRBG

 * to that of the cipher.

 *

 * TODO(DRBG): would be nice to have the strength configurable

 * RAND_DRBG_STRENGTH is currently only used for the legacy RAND

 * implementation.

 *

 * Currently supported ciphers are: NID_aes_128_ctr, NID_aes_192_ctr and

 * NID_aes_256_ctr

 *

 * TODO(DRBG): would be nice to have the NID and strength configurable

 */

# define RAND_DRBG_STRENGTH             128

# define RAND_DRBG_NID                  NID_aes_128_ctr

# define RAND_DRBG_STRENGTH             256

# define RAND_DRBG_NID                  NID_aes_256_ctr

/*

 * Object lifetime functions.