X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/079b0efce92f6d74eab3d2c0fb4930b822b96393..HEAD:/symm/gcm-arm-crypto.S

diff --git a/symm/gcm-arm-crypto.S b/symm/gcm-arm-crypto.S
index 166a5b74..8494e42b 100644
--- a/symm/gcm-arm-crypto.S
+++ b/symm/gcm-arm-crypto.S
@@ -67,7 +67,14 @@
 	//	    = SUM_{0<=i,j<n} u_i v_j t^{2n-2-(i+j)}
 	//
 	// which is almost the bit-reversal of u v, only it's shifted right
-	// by one place.  Oh, well: we'll have to shift it back later.
+	// by one place.  Putting this another way, what we have is actually
+	// the bit reversal of the product u v t.  We could get the correct
+	// answer (modulo p(t)) if we'd sneakily divided one of the operands
+	// by t before we started.  Conveniently, v is actually the secret
+	// value k set up by the GCM `mktable' function, so we can arrange to
+	// actually store k/t (mod p(t)) and then the product will come out
+	// correct (modulo p(t)) and we won't have anything more to worry
+	// about here.
 	//
 	// That was important to think about, but there's not a great deal to
 	// do about it yet other than to convert what we've got from the
@@ -92,109 +99,66 @@
 	// use Karatsuba's identity here, but I suspect that loses more in
 	// the shifting, bit-twiddling, and dependency chains that it gains
 	// in saving a multiplication which otherwise pipelines well.
-	// q0 =				// (u_0; u_1)
-	// q1 =				// (v_0; v_1)
+	// q0 =				// (u_1; u_0)
+	// q1 =				// (v_1; v_0)
 	vmull.p64 q2, d1, d2		// u_1 v_0
 	vmull.p64 q3, d0, d3		// u_0 v_1
-	vmull.p64 q8, d1, d3		// (x_3; t_1) = u_1 v_1
-	vmull.p64 q9, d0, d2		// (t_0; x_0) = u_0 v_0
+	vmull.p64 q8, d1, d3		// (t_1; x_3) = u_1 v_1
+	vmull.p64 q9, d0, d2		// (x_0; t_0) = u_0 v_0
 
 	// Arrange the pieces to form a double-precision polynomial.
-	veor	q2, q2, q3		// (m_1; m_0) = u_0 v_1 + u_1 v_0
+	veor	q2, q2, q3		// (m_0; m_1) = u_0 v_1 + u_1 v_0
 	veor	d17, d17, d4		// x_2 = t_1 + m_1
 	veor	d18, d18, d5		// x_1 = t_0 + m_0
-	// q8 =				// (x_3; x_2)
-	// q9 =				// (x_1; x_0)
+	// q8 =				// (x_2; x_3)
+	// q9 =				// (x_0; x_1)
 
-	// Two-and-a-half problems remain.  The first is that this product is
-	// shifted left by one place, which is annoying.  Let's take care of
-	// that now.  Once this is done, we'll be properly in GCM's backwards
-	// bit-ordering.
+	// One-and-a-half problems remain.
 	//
-	// The half a problem is that the result wants to have its 64-bit
-	// halves switched.  Here turns out to be the best place to arrange
-	// for that.
+	// The full-size problem is that the result needs to be reduced
+	// modulo p(t) = t^128 + t^7 + t^2 + t + 1.  Let R = t^128 = t^7 +
+	// t^2 + t + 1 in our field.  So far, we've calculated z_0 and z_1
+	// such that z_0 + z_1 R = u v using the identity R = t^128: now we
+	// must collapse the two halves of y together using the other
+	// identity R = t^7 + t^2 + t + 1.
 	//
-	//		     q9				    q8
-	//	,-------------.-------------.  ,-------------.-------------.
-	//	| 0  x_0-x_62 | x_63-x_126  |  | x_127-x_190 | x_191-x_254 |
-	//	`-------------^-------------'  `-------------^-------------'
-	//	      d19	    d18		     d17	   d16
-	//
-	// We start by shifting each 32-bit lane right (from GCM's point of
-	// view -- physically, left) by one place, which gives us this:
-	//
-	//		   low (q9)			 high (q8)
-	//	,-------------.-------------.  ,-------------.-------------.
-	//	| x_0-x_62  0 |x_64-x_126 0 |  |x_128-x_190 0|x_192-x_254 0|
-	//	`-------------^-------------'  `-------------^-------------'
-	//	      d19	    d18		     d17	   d16
-	//
-	// but we've lost a bunch of bits.  We separately shift each lane
-	// left by 31 places to give us the bits we lost.
-	//
-	//		   low (q3)			 high (q2)
-	//	,-------------.-------------.  ,-------------.-------------.
-	//	|    0...0    | 0...0  x_63 |  | 0...0 x_127 | 0...0 x_191 |
-	//	`-------------^-------------'  `-------------^-------------'
-	//			     d6		     d5		   d4
-	//
-	// Since we can address each of these pieces individually, putting
-	// them together is relatively straightforward.
-
-
-	vshr.u64 d6, d18, #63		// shifted left; just the carries
-	vshl.u64 q9, q9, #1		// shifted right, but dropped carries
-	vshr.u64 q2, q8, #63
-	vshl.u64 q8, q8, #1
-	vorr	d0, d19, d6		// y_0
-	vorr	d1, d18, d5		// y_1
-	vorr	d2, d17, d4		// y_2
-	vmov	d3, d16			// y_3
-
-	// And the other one is that the result needs to be reduced modulo
-	// p(t) = t^128 + t^7 + t^2 + t + 1.  Let R = t^128 = t^7 + t^2 + t +
-	// 1 in our field.  So far, we've calculated z_0 and z_1 such that
-	// z_0 + z_1 R = u v using the identity R = t^128: now we must
-	// collapse the two halves of y together using the other identity R =
-	// t^7 + t^2 + t + 1.
-	//
-	// We do this by working on y_2 and y_3 separately, so consider y_i
-	// for i = 2 or 3.  Certainly, y_i t^{64i} = y_i R t^{64(i-2) =
-	// (t^7 + t^2 + t + 1) y_i t^{64(i-2)}, but we can't use that
+	// We do this by working on x_2 and x_3 separately, so consider x_i
+	// for i = 2 or 3.  Certainly, x_i t^{64i} = x_i R t^{64(i-2) =
+	// (t^7 + t^2 + t + 1) x_i t^{64(i-2)}, but we can't use that
 	// directly without breaking up the 64-bit word structure.  Instead,
-	// we start by considering just y_i t^7 t^{64(i-2)}, which again
-	// looks tricky.  Now, split y_i = a_i + t^57 b_i, with deg a_i < 57;
+	// we start by considering just x_i t^7 t^{64(i-2)}, which again
+	// looks tricky.  Now, split x_i = a_i + t^57 b_i, with deg a_i < 57;
 	// then
 	//
-	//	y_i t^7 t^{64(i-2)} = a_i t^7 t^{64(i-2)} + b_i t^{64(i-1)}
+	//	x_i t^7 t^{64(i-2)} = a_i t^7 t^{64(i-2)} + b_i t^{64(i-1)}
 	//
-	// We can similarly decompose y_i t^2 and y_i t into a pair of 64-bit
+	// We can similarly decompose x_i t^2 and x_i t into a pair of 64-bit
 	// contributions to the t^{64(i-2)} and t^{64(i-1)} words, but the
 	// splits are different.  This is lovely, with one small snag: when
-	// we do this to y_3, we end up with a contribution back into the
+	// we do this to x_3, we end up with a contribution back into the
 	// t^128 coefficient word.  But notice that only the low seven bits
 	// of this word are affected, so there's no knock-on contribution
 	// into the t^64 word.  Therefore, if we handle the high bits of each
 	// word together, and then the low bits, everything will be fine.
 
 	// First, shift the high bits down.
-	vshl.u64 q2, q1, #63		// the b_i for t
-	vshl.u64 q3, q1, #62		// the b_i for t^2
-	vshl.u64 q8, q1, #57		// the b_i for t^7
+	vshl.u64 q2, q8, #63		// the b_i for t
+	vshl.u64 q3, q8, #62		// the b_i for t^2
+	vshl.u64 q0, q8, #57		// the b_i for t^7
 	veor	q2, q2, q3		// add them all together
-	veor	q2, q2, q8
-	veor	d2, d2, d5		// contribution into low half
-	veor	d1, d1, d4		// and high half
+	veor	q2, q2, q0
+	veor	d18, d18, d5		// contribution into low half
+	veor	d17, d17, d4		// and high half
 
 	// And then shift the low bits up.
-	vshr.u64 q2, q1, #1
-	vshr.u64 q3, q1, #2
-	vshr.u64 q8, q1, #7
-	veor	q0, q0, q1		// mix in the unit contribution
+	vshr.u64 q2, q8, #1
+	vshr.u64 q3, q8, #2
+	vshr.u64 q1, q8, #7
+	veor	q8, q8, q9		// mix in the unit contribution
 	veor	q2, q2, q3		// t and t^2 contribs
-	veor	q0, q0, q8		// low, unit, and t^7 contribs
-	veor	q0, q0, q2		// mix them together and we're done
+	veor	q1, q1, q8		// low, unit, and t^7 contribs
+	veor	d1, d2, d4		// mix them together and swap halves
+	veor	d0, d3, d5
 .endm
 
 .macro	mul64
@@ -204,29 +168,22 @@
 	// The multiplication is thankfully easy.
 	vmull.p64 q0, d0, d1		// u v
 
-	// Shift the product up by one place, and swap the two halves.  After
-	// this, we're in GCM bizarro-world.
-	vshr.u64 d2, d0, #63		// shifted left; just the carries
-	vshl.u64 d3, d1, #1		// low half right
-	vshl.u64 d1, d0, #1		// high half shifted right
-	vorr	d0, d3, d2		// mix in the carries
-
 	// Now we must reduce.  This is essentially the same as the 128-bit
 	// case above, but mostly simpler because everything is smaller.  The
 	// polynomial this time is p(t) = t^64 + t^4 + t^3 + t + 1.
 
 	// First, shift the high bits down.
-	vshl.u64 d2, d1, #63		// b_i for t
-	vshl.u64 d3, d1, #61		// b_i for t^3
-	vshl.u64 d4, d1, #60		// b_i for t^4
+	vshl.u64 d2, d0, #63		// b_i for t
+	vshl.u64 d3, d0, #61		// b_i for t^3
+	vshl.u64 d4, d0, #60		// b_i for t^4
 	veor	d2, d2, d3		// add them all together
 	veor	d2, d2, d4
-	veor	d1, d1, d2		// contribution back into high half
+	veor	d0, d0, d2		// contribution back into high half
 
 	// And then shift the low bits up.
-	vshr.u64 d2, d1, #1
-	vshr.u64 d3, d1, #3
-	vshr.u64 d4, d1, #4
+	vshr.u64 d2, d0, #1
+	vshr.u64 d3, d0, #3
+	vshr.u64 d4, d0, #4
 	veor	d0, d0, d1		// mix in the unit contribution
 	veor	d2, d2, d3		// t and t^3 contribs
 	veor	d0, d0, d4		// low, unit, and t^4
@@ -240,16 +197,12 @@
 	// word.  Clobbers q1--q3, q8, q9.
 
 	// This is an inconvenient size.  There's nothing for it but to do
-	// four multiplications, as if for the 128-bit case.  It's possible
-	// that there's cruft in the top 32 bits of the input registers, so
-	// shift both of them up by four bytes before we start.  This will
-	// mean that the high 64 bits of the result (from GCM's viewpoint)
-	// will be zero.
-	// q0 =				// (u_0 + u_1 t^32; u_2)
-	// q1 =				// (v_0 + v_1 t^32; v_2)
+	// four multiplications, as if for the 128-bit case.
+	// q0 =				// (u_2; u_0 + u_1 t^32)
+	// q1 =				// (v_2; v_0 + v_1 t^32)
 	vmull.p64 q8, d1, d2		// u_2 (v_0 + v_1 t^32) = e_0
 	vmull.p64 q9, d0, d3		// v_2 (u_0 + u_1 t^32) = e_1
-	vmull.p64 q3, d1, d3		// u_2 v_2 t^64 = d = (0; d)
+	vmull.p64 q3, d1, d3		// u_2 v_2 t^64 = d = (d; 0)
 	vmull.p64 q0, d0, d2		// u_0 v_0 + (u_0 v_1 + u_1 v_0) t^32
 					//   + u_1 v_1 t^64 = f
 
@@ -271,20 +224,6 @@
 	veor	d0, d0, d17		// q0 = bot([d t^128] + e t^64 + f)
 	veor	d3, d3, d16		// q1 = top(d t^128 + e t^64 + f)
 
-	// Shift the product right by one place (from GCM's point of view),
-	// but, unusually, don't swap the halves, because we need to work on
-	// the 32-bit pieces later.  After this, we're in GCM bizarro-world.
-	// q0 =				// (?, x_2; x_1, x_0)
-	// q1 =				// (0, x_5; x_4, x_3)
-	vshr.u64 d4, d0, #63		// carry from d0 to d1
-	vshr.u64 d5, d2, #63		// carry from d2 to d3
-	vshr.u32 d6, d3, #31		// carry from d3 to d0
-	vshl.u64 q0, q0, #1		// shift low half
-	vshl.u64 q1, q1, #1		// shift high half
-	vorr	d1, d1, d4
-	vorr	d0, d0, d6
-	vorr	d3, d3, d5
-
 	// Finally, the reduction.  This is essentially the same as the
 	// 128-bit case, except that the polynomial is p(t) = t^96 + t^10 +
 	// t^9 + t^6 + 1.  The degrees are larger but not enough to cause
@@ -340,37 +279,24 @@
 	 veor	q11, q11, q13		// b = u_1 v_2 + u_2 v_1
 
 	// Piece the product together.
-	veor	d17, d17, d22  //  q8 =	// (x_5; x_4)
+	veor	d17, d17, d22  //  q8 =	// (x_4; x_5)
 	veor	d18, d18, d23
-	veor	d19, d19, d24  //  q9 =	// (x_3; x_2)
-	veor	d20, d20, d25  // q10 =	// (x_1; x_0)
-
-	// Shift the product right by one place (from GCM's point of view).
-	vshr.u64 q11, q8, #63		// carry from d16/d17 to d17/d18
-	vshr.u64 q12, q9, #63		// carry from d18/d19 to d19/d20
-	vshr.u64 d26, d20, #63		// carry from d20 to d21
-	vshl.u64 q8, q8, #1		// shift everything down
-	vshl.u64 q9, q9, #1
-	vshl.u64 q10, q10, #1
-	vorr	d17, d17, d22		// and mix in the carries
-	vorr	d18, d18, d23
-	vorr	d19, d19, d24
-	vorr	d20, d20, d25
-	vorr	d21, d21, d26
+	veor	d19, d19, d24  //  q9 =	// (x_2; x_3)
+	veor	d20, d20, d25  // q10 =	// (x_0; x_1)
 
 	// Next, the reduction.  Our polynomial this time is p(x) = t^192 +
 	// t^7 + t^2 + t + 1.  Yes, the magic numbers are the same as the
 	// 128-bit case.  I don't know why.
 
 	// First, shift the high bits down.
-	// q8 =				// (y_5; y_4)
-	// q9 =				// (y_3; y_2)
-	// q10 =			// (y_1; y_0)
-	vshl.u64 q11, q8, #63		// (y_5; y_4) b_i for t
+	// q8 =				// (y_4; y_5)
+	// q9 =				// (y_2; y_3)
+	// q10 =			// (y_0; y_1)
+	vshl.u64 q11, q8, #63		// (y_4; y_5) b_i for t
 	vshl.u64 d28, d18, #63		// y_3 b_i for t
-	vshl.u64 q12, q8, #62		// (y_5; y_4) b_i for t^2
+	vshl.u64 q12, q8, #62		// (y_4; y_5) b_i for t^2
 	vshl.u64 d29, d18, #62		// y_3 b_i for t^2
-	vshl.u64 q13, q8, #57		// (y_5; y_4) b_i for t^7
+	vshl.u64 q13, q8, #57		// (y_4; y_5) b_i for t^7
 	vshl.u64 d30, d18, #57		// y_3 b_i for t^7
 	veor	q11, q11, q12		// mix them all together
 	veor	d28, d28, d29
@@ -381,14 +307,14 @@
 
 	// And finally shift the low bits up.  Also, switch the order of the
 	// pieces for output.
-	// q8 =				// (y'_5; y'_4)
-	// q9 =				// (y'_3; y'_2)
-	// q10 =			// (y'_1; y'_0)
-	vshr.u64 q11, q8, #1		// (y_5; y_4) a_i for t
+	// q8 =				// (y'_4; y'_5)
+	// q9 =				// (y'_2; y'_3)
+	// q10 =			// (y'_0; y'_1)
+	vshr.u64 q11, q8, #1		// (y_4; y_5) a_i for t
 	vshr.u64 d28, d18, #1		// y'_3 a_i for t
-	vshr.u64 q12, q8, #2		// (y_5; y_4) a_i for t^2
+	vshr.u64 q12, q8, #2		// (y_4; y_5) a_i for t^2
 	vshr.u64 d29, d18, #2		// y'_3 a_i for t^2
-	vshr.u64 q13, q8, #7		// (y_5; y_4) a_i for t^7
+	vshr.u64 q13, q8, #7		// (y_4; y_5) a_i for t^7
 	vshr.u64 d30, d18, #7		// y'_3 a_i for t^7
 	veor	q8, q8, q11
 	veor	d18, d18, d28
@@ -415,20 +341,20 @@
 	//
 	//	q = r s = (u_0 + u_1) (v_0 + v_1)
 	//	  = (u_0 v_0) + (u1 v_1) + (u_0 v_1 + u_1 v_0)
-	//	  = a + d + c
+	//	  = a + c + b
 	//
 	// The first two terms we've already calculated; the last is the
 	// remaining one we want.  We'll set B = t^128.  We know how to do
 	// 128-bit multiplications already, and Karatsuba is too annoying
 	// there, so there'll be 12 multiplications altogether, rather than
 	// the 16 we'd have if we did this the naïve way.
-	// q0 =				// u_0 = (u_00; u_01)
-	// q1 =				// u_1 = (u_10; u_11)
-	// q2 =				// v_0 = (v_00; v_01)
-	// q3 =				// v_1 = (v_10; v_11)
+	// q0 =				// u_0 = (u_01; u_00)
+	// q1 =				// u_1 = (u_11; u_10)
+	// q2 =				// v_0 = (v_01; v_00)
+	// q3 =				// v_1 = (v_11; v_10)
 
-	veor	q8, q0, q1		// u_* = (u_00 + u_10; u_01 + u_11)
-	veor	q9, q2, q3		// v_* = (v_00 + v_10; v_01 + v_11)
+	veor	q8, q0, q1		// u_* = (u_01 + u_11; u_00 + u_10)
+	veor	q9, q2, q3		// v_* = (v_01 + v_11; v_00 + v_10)
 
 	// Start by building the cross product, q = u_* v_*.
 	vmull.p64 q14, d16, d19		// u_*0 v_*1
@@ -467,38 +393,21 @@
 	veor	q9, q9, q12
 	veor	q10, q10, q13
 
-	// Shift the product right by one place (from GCM's point of view).
-	vshr.u64 q0, q8, #63		// carry from d16/d17 to d17/d18
-	vshr.u64 q1, q9, #63		// carry from d18/d19 to d19/d20
-	vshr.u64 q2, q10, #63		// carry from d20/d21 to d21/d22
-	vshr.u64 d6, d22, #63		// carry from d22 to d23
-	vshl.u64 q8, q8, #1		// shift everyting down
-	vshl.u64 q9, q9, #1
-	vshl.u64 q10, q10, #1
-	vshl.u64 q11, q11, #1
-	vorr	d17, d17, d0
-	vorr	d18, d18, d1
-	vorr	d19, d19, d2
-	vorr	d20, d20, d3
-	vorr	d21, d21, d4
-	vorr	d22, d22, d5
-	vorr	d23, d23, d6
-
 	// Now we must reduce.  This is essentially the same as the 192-bit
 	// case above, but more complicated because everything is bigger.
 	// The polynomial this time is p(t) = t^256 + t^10 + t^5 + t^2 + 1.
 
 	// First, shift the high bits down.
-	// q8 =				// (y_7; y_6)
-	// q9 =				// (y_5; y_4)
-	// q10 =			// (y_3; y_2)
-	// q11 =			// (y_1; y_0)
-	vshl.u64 q0, q8, #62		// (y_7; y_6) b_i for t^2
-	vshl.u64 q12, q9, #62		// (y_5; y_4) b_i for t^2
-	vshl.u64 q1, q8, #59		// (y_7; y_6) b_i for t^5
-	vshl.u64 q13, q9, #59		// (y_5; y_4) b_i for t^5
-	vshl.u64 q2, q8, #54		// (y_7; y_6) b_i for t^10
-	vshl.u64 q14, q9, #54		// (y_5; y_4) b_i for t^10
+	// q8 =				// (y_6; y_7)
+	// q9 =				// (y_4; y_5)
+	// q10 =			// (y_2; y_3)
+	// q11 =			// (y_0; y_1)
+	vshl.u64 q0, q8, #62		// (y_6; y_7) b_i for t^2
+	vshl.u64 q12, q9, #62		// (y_4; y_5) b_i for t^2
+	vshl.u64 q1, q8, #59		// (y_6; y_7) b_i for t^5
+	vshl.u64 q13, q9, #59		// (y_4; y_5) b_i for t^5
+	vshl.u64 q2, q8, #54		// (y_6; y_7) b_i for t^10
+	vshl.u64 q14, q9, #54		// (y_4; y_5) b_i for t^10
 	veor	q0, q0, q1		// mix the contributions together
 	veor	q12, q12, q13
 	veor	q0, q0, q2
@@ -510,16 +419,16 @@
 
 	// And then shift the low bits up.  Also, switch the order of the
 	// pieces for output.
-	// q8 =				// (y'_7; y'_6)
-	// q9 =				// (y'_5; y'_4)
-	// q10 =			// (y'_3; y'_2)
-	// q11 =			// (y'_1; y'_0)
-	vshr.u64 q0, q8, #2		// (y_7; y_6) a_i for t^2
-	vshr.u64 q12, q9, #2		// (y_5; y'_4) a_i for t^2
-	vshr.u64 q1, q8, #5		// (y_7; y_6) a_i for t^5
-	vshr.u64 q13, q9, #5		// (y_5; y_4) a_i for t^5
-	vshr.u64 q2, q8, #10		// (y_7; y_6) a_i for t^10
-	vshr.u64 q14, q9, #10		// (y_5; y_4) a_i for t^10
+	// q8 =				// (y'_6; y'_7)
+	// q9 =				// (y'_4; y'_5)
+	// q10 =			// (y'_2; y'_3)
+	// q11 =			// (y'_0; y'_1)
+	vshr.u64 q0, q8, #2		// (y_6; y_7) a_i for t^2
+	vshr.u64 q12, q9, #2		// (y'_4; y_5) a_i for t^2
+	vshr.u64 q1, q8, #5		// (y_6; y_7) a_i for t^5
+	vshr.u64 q13, q9, #5		// (y_4; y_5) a_i for t^5
+	vshr.u64 q2, q8, #10		// (y_6; y_7) a_i for t^10
+	vshr.u64 q14, q9, #10		// (y_4; y_5) a_i for t^10
 
 	veor	q8, q8, q0		// mix the contributions together
 	veor	q1, q1, q2