}

// Used in the key schedule to produce each subkey by selecting 48 bits from
// the 56-bit input
var permutedChoice2 = [48]byte{
	42, 39, 45, 32, 55, 51, 53, 28,
	41, 50, 35, 46, 33, 37, 44, 52,
	30, 48, 40, 49, 29, 36, 43, 54,
	15, 4, 25, 19, 9, 1, 26, 16,
	5, 11, 23, 8, 12, 7, 17, 0,
	22, 3, 10, 14, 6, 20, 27, 24,
}

// 8 S-boxes composed of 4 rows and 16 columns
// Used in the DES cipher function

		// combine halves to form 56-bit input to PC2
		pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
		// apply PC2 permutation to 7 byte input
		c.subkeys[i] = unpack(permuteBlock(pc2Input, permutedChoice2[:]))
	}
}

// Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top.