[Cryptech-Commits] [user/shatov/ecdsa_fpga_model] branch master updated: Minor cleanup

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meisterpaul1 at yandex.ru pushed a commit to branch master
in repository user/shatov/ecdsa_fpga_model.

The following commit(s) were added to refs/heads/master by this push:
     new cae8718  Minor cleanup
cae8718 is described below

commit cae8718217846cfaefcbfecd55f9a117731a8d99
Author: Pavel V. Shatov (Meister) <meisterpaul1 at yandex.ru>
AuthorDate: Mon Feb 6 14:40:16 2017 +0300

    Minor cleanup
    
     * Fixed misplaced comma in 'ecdsa_model.h'
     * Rewrote P-384 reduction routine to match the style used in P-256 reduction
---
 ecdsa_model.h    |  4 ++--
 fpga_modular.cpp | 33 ++++++++++++++++++++-------------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/ecdsa_model.h b/ecdsa_model.h
index 1e6a04c..fc7e571 100644
--- a/ecdsa_model.h
+++ b/ecdsa_model.h
@@ -45,7 +45,7 @@
 // USE_CURVE == 2  -> P-384
 //
 //------------------------------------------------------------------------------
-#define USE_CURVE	1
+#define USE_CURVE	2
 
 
 //------------------------------------------------------------------------------
@@ -112,7 +112,7 @@
 #define P_384_ONE		{0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000001}
 
 /* Division Factor  */
-#define P_384_DELTA		{0x7fffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0x7fffffff, 0x80000000, 0x0000000, 0x080000000}
+#define P_384_DELTA		{0x7fffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0xffffffff, 0x7fffffff, 0x80000000, 0x00000000, 0x80000000}
 
 /* Base Point */
 #define P_384_G_X		{0xaa87ca22, 0xbe8b0537, 0x8eb1c71e, 0xf320ad74, 0x6e1d3b62, 0x8ba79b98, 0x59f741e0, 0x82542a38, 0x5502f25d, 0xbf55296c, 0x3a545e38, 0x72760ab7}
diff --git a/fpga_modular.cpp b/fpga_modular.cpp
index af485a0..9b01df0 100644
--- a/fpga_modular.cpp
+++ b/fpga_modular.cpp
@@ -605,7 +605,8 @@ void fpga_modular_mul_helper_reduce_p256(FPGA_WORD *c, FPGA_BUFFER *p)
 // on the other hand is the output of the parallelized Comba multiplier, so it
 // is 2*OPERAND_WIDTH wide and has twice as many words (2*OPERAND_NUM_WORDS).
 //
-// ...
+// To save FPGA resources, the calculation is done using only two adders and
+// one subtractor. The algorithm is split into five steps.
 //
 //------------------------------------------------------------------------------
 #if USE_CURVE == 2
@@ -626,27 +627,33 @@ void fpga_modular_mul_helper_reduce_p384(FPGA_WORD *c, FPGA_BUFFER *p)
 	 s9.words[11] = 0,       s9.words[10] = 0,       s9.words[ 9] = 0,       s9.words[ 8] = 0,       s9.words[ 7] = 0,       s9.words[ 6] = 0,       s9.words[ 5] = 0,       s9.words[ 4] = c[23],   s9.words[ 3] = c[22],   s9.words[ 2] = c[21],   s9.words[ 1] = c[20],   s9.words[ 0] = 0;
 	s10.words[11] = 0,      s10.words[10] = 0,      s10.words[ 9] = 0,      s10.words[ 8] = 0,      s10.words[ 7] = 0,      s10.words[ 6] = 0,      s10.words[ 5] = 0,      s10.words[ 4] = c[23],  s10.words[ 3] = c[23],  s10.words[ 2] = 0,      s10.words[ 1] = 0,      s10.words[ 0] = 0;
 
-
 		// intermediate results
-	FPGA_BUFFER t1, t2, t3, t4;
+	FPGA_BUFFER sum0, sum1, difference;
 
 		/* Step 1. */
-	fpga_modular_add(&s1,  &s3, &t1);	// t1 = s1 + s3
-	fpga_modular_add(&s2,  &s2, &t2);	// t2 = 2*s2
-	fpga_modular_add(&s4,  &s5, &t3);	// t3 = s4 + s5
-	fpga_modular_add(&s6,  &s7, &t4);	// t4 = s6 + s7
+	fpga_modular_add(&s1,         &s3,         &sum0);			// sum0 = s1 + s3
+	fpga_modular_add(&s2,         &s2,         &sum1);			// sum1 = 2*s2
+	fpga_modular_sub(&ecdsa_zero, &s8,         &difference);	// difference = -s8
 
 		/* Step 2. */
-	fpga_modular_add(&t1,  &t2, &t1);	// t1 = t1 + t2 = s1 + 2*s2 + 2*s3
-	fpga_modular_add(&t3,  &t4, &t2);	// t2 = t3 + t4 = s4 + s5 + s6 + s7
-	fpga_modular_add(&s8,  &s9, &t3);	// t3 = s8 + s9
+	fpga_modular_add(&sum0,       &s4,         &sum0);			// sum0 = s1 + s3 + s4
+	fpga_modular_add(&sum1,       &s5,         &sum1);			// sum1 = 2*s2 + s5
+	fpga_modular_sub(&difference, &s9,         &difference);	// difference = -(s8 + s9)
 
 		/* Step 3. */
-	fpga_modular_add(&t1,  &t2, &t1);	// t1 = t1 + t2 = s1 + 2*s2 + 2*s3 + s4 + s5 + s6 + s7
-	fpga_modular_add(&s10, &t3, &t2);	// t2 = s10 + t3 = s8 + s9 + s10
+	fpga_modular_add(&sum0,       &s6,         &sum0);			// sum0 = s1 + s3 + s4 + s6
+	fpga_modular_add(&sum1,       &s7,         &sum1);			// sum1 = 2*s2 + s5 + s7
+	fpga_modular_sub(&difference, &s10,        &difference);	// difference = -(s8 + s9 + s10)
 
 		/* Step 4. */
-	fpga_modular_sub(&t1,  &t2, p);		// p = t1 - t2 = s1 + 2*s2 + 2*s3 + s4 + s5 + s6 + s7 - s8 - s9 - s10
+	fpga_modular_add(&sum0,       &sum1,       &sum0);			// sum0 = s1 + 2*s2 + 2*s3 + s4 + s5
+//	fpga_modular_add(<dummy>,     <dummy>,     &sum1);			// dummy cycle, result ignored
+	fpga_modular_sub(&difference, &ecdsa_zero, &difference);	// compulsory cycle to keep difference constant for next stage
+
+		/* Step 5. */
+	fpga_modular_add(&sum0,       &difference, p);				// p = s1 + 2*s2 + s3 + s4 + s5 + s6 + s7 - s8 - s9 - s10
+//	fpga_modular_add(<dummy>,     <dummy>,     &sum1);			// dummy cycle, result ignored
+//	fpga_modular_add(<dummy>,     <dummy>,     &difference);	// dummy cycle, result ignored
 }
 #endif
 

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