Add polynomial for 1024-bit block cipher.

This will support Threefish and its 1024-bit block size. I believe this is correct, but it may be wrong. According to "Table of Low-Weight Binary Irreducible Polynomials" (http://www.hpl.hp.com/techreports/98/HPL-98-135.pdf), the polynomial is x^1024 + x^19 + x^6 + x + 1.

1 files changed, 10 insertions, 1 deletions

diff --git a/cmac.cpp b/cmac.cpp
index ca04d0bd..81047827 100644
--- a/cmac.cpp
+++ b/cmac.cpp
@@ -31,15 +31,24 @@ static void MulU(byte *k, unsigned int length)
 			k[15] ^= 0x87;

 			break;

 		case 32:

-			// Should this be 0x425?

+			// https://crypto.stackexchange.com/q/9815/10496

+			// Polynomial x^256 + x^10 + x^5 + x + 1

 			k[30] ^= 4;

 			k[31] ^= 0x23;

 			break;

 		case 64:

 			// https://crypto.stackexchange.com/q/9815/10496

+			// Polynomial x^512 + x^8 + x^5 + x^2 + 1

 			k[62] ^= 1;

 			k[63] ^= 0x25;

 			break;

+		case 128:

+			// https://crypto.stackexchange.com/q/9815/10496

+			// Polynomial x^1024 + x^19 + x^6 + x + 1

+			k[126] ^= 8;

+			k[126] ^= 0x00;

+			k[127] ^= 0x43;

+			break;

 		default:

 			throw InvalidArgument("CMAC: " + IntToString(length) + " is not a supported cipher block size");

 		}