Yes, sorry. You need to overwrite the initial value (H0) too, in the constructor. You can do that if you can touch the equivalent of the private member variable

Yes, sorry. You need to overwrite the initial value (H0) too, in the constructor. You can do that if you can touch the equivalent of the private member variables. SHA-512/256 may be used to hash a message, M, having a length of 𝓁 bits, where 128 0 ≤ 𝓁 < 2. The algorithm is defined in the exact same manner as SHA-512 (Sec. 6.4), with the following two exceptions: 1. The initial hash value, H(0), shall be set as specified in Sec. 5.3.6.2; and 2. The 256-bit message digest is obtained by truncating the final hash value, H(N), to its left-most 256 bits. (from §6.7 in http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4....) EDIT: I trust 'tptacek (in sibling comment) that if there is no chance of protocol confusion, there is no advantage to the different initial value.