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Thumb2 X25519: Fix to do full reduction

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This fix when into ARM32 assembly it is now being added to Thumb2 assembly.
Full reduction to ensure the number is in range at end of work.
This commit is contained in:
Sean Parkinson
2026-06-18 20:34:11 +10:00
parent 633784e91b
commit ad85f49926
2 changed files with 70 additions and 8 deletions
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wolfcrypt/src/port/arm/thumb2-curve25519.S
+36 -5
View File
@@ -2933,10 +2933,33 @@ L_curve25519_inv_8:
LDR r1, [sp, #160]
LDR r0, [sp, #160]
BL fe_mul_op
/* Ensure result is less than modulus */
LDR r0, [sp, #160]
LDM r0, {r4, r5, r6, r7, r8, r9, r10, r11}
ADDS r2, r4, #0x13
ADCS r2, r5, #0x0
ADCS r2, r6, #0x0
ADCS r2, r7, #0x0
ADCS r2, r8, #0x0
ADCS r2, r9, #0x0
ADCS r2, r10, #0x0
ADC r2, r11, #0x0
ASR r2, r2, #31
AND r2, r2, #0x13
ADDS r4, r4, r2
ADCS r5, r5, #0x0
ADCS r6, r6, #0x0
ADCS r7, r7, #0x0
ADCS r8, r8, #0x0
ADCS r9, r9, #0x0
ADCS r10, r10, #0x0
ADC r11, r11, #0x0
BFC r11, #31, #1
STM r0, {r4, r5, r6, r7, r8, r9, r10, r11}
MOV r0, #0x0
ADD sp, sp, #0xbc
POP {r4, r5, r6, r7, r8, r9, r10, r11, pc}
/* Cycle Count = 682 */
/* Cycle Count = 721 */
.size curve25519,.-curve25519
#else
.text
@@ -3253,22 +3276,30 @@ L_curve25519_inv_8:
/* Ensure result is less than modulus */
LDR r0, [sp, #176]
LDM r0, {r4, r5, r6, r7, r8, r9, r10, r11}
MOV r2, #0x13
AND r2, r2, r11, ASR #31
ADDS r2, r4, #0x13
ADCS r2, r5, #0x0
ADCS r2, r6, #0x0
ADCS r2, r7, #0x0
ADCS r2, r8, #0x0
ADCS r2, r9, #0x0
ADCS r2, r10, #0x0
ADC r2, r11, #0x0
ASR r2, r2, #31
AND r2, r2, #0x13
ADDS r4, r4, r2
ADCS r5, r5, #0x0
ADCS r6, r6, #0x0
ADCS r7, r7, #0x0
ADCS r8, r8, #0x0
ADCS r9, r9, #0x0
BFC r11, #31, #1
ADCS r10, r10, #0x0
ADC r11, r11, #0x0
BFC r11, #31, #1
STM r0, {r4, r5, r6, r7, r8, r9, r10, r11}
MOV r0, #0x0
ADD sp, sp, #0xc0
POP {r4, r5, r6, r7, r8, r9, r10, r11, pc}
/* Cycle Count = 589 */
/* Cycle Count = 597 */
.size curve25519,.-curve25519
#endif /* WC_NO_CACHE_RESISTANT */
#endif /* HAVE_CURVE25519 */
wolfcrypt/src/port/arm/thumb2-curve25519_c.c
+34 -3
View File
@@ -3372,6 +3372,29 @@ WC_OMIT_FRAME_POINTER int curve25519(byte* r, const byte* n, const byte* a)
"LDR r1, [sp, #160]\n\t"
"LDR r0, [sp, #160]\n\t"
"BL fe_mul_op\n\t"
/* Ensure result is less than modulus */
"LDR %[r], [sp, #160]\n\t"
"LDM %[r], {r4, r5, r6, r7, r8, r9, r10, r11}\n\t"
"ADDS %[a], r4, #0x13\n\t"
"ADCS %[a], r5, #0x0\n\t"
"ADCS %[a], r6, #0x0\n\t"
"ADCS %[a], r7, #0x0\n\t"
"ADCS %[a], r8, #0x0\n\t"
"ADCS %[a], r9, #0x0\n\t"
"ADCS %[a], r10, #0x0\n\t"
"ADC %[a], r11, #0x0\n\t"
"ASR %[a], %[a], #31\n\t"
"AND %[a], %[a], #0x13\n\t"
"ADDS r4, r4, %[a]\n\t"
"ADCS r5, r5, #0x0\n\t"
"ADCS r6, r6, #0x0\n\t"
"ADCS r7, r7, #0x0\n\t"
"ADCS r8, r8, #0x0\n\t"
"ADCS r9, r9, #0x0\n\t"
"ADCS r10, r10, #0x0\n\t"
"ADC r11, r11, #0x0\n\t"
"BFC r11, #31, #1\n\t"
"STM %[r], {r4, r5, r6, r7, r8, r9, r10, r11}\n\t"
"MOV r0, #0x0\n\t"
"ADD sp, sp, #0xbc\n\t"
#ifndef WOLFSSL_NO_VAR_ASSIGN_REG
@@ -3773,17 +3796,25 @@ WC_OMIT_FRAME_POINTER int curve25519(byte* r, const byte* n, const byte* a)
/* Ensure result is less than modulus */
"LDR %[r], [sp, #176]\n\t"
"LDM %[r], {r4, r5, r6, r7, r8, r9, r10, r11}\n\t"
"MOV %[a], #0x13\n\t"
"AND %[a], %[a], r11, ASR #31\n\t"
"ADDS %[a], r4, #0x13\n\t"
"ADCS %[a], r5, #0x0\n\t"
"ADCS %[a], r6, #0x0\n\t"
"ADCS %[a], r7, #0x0\n\t"
"ADCS %[a], r8, #0x0\n\t"
"ADCS %[a], r9, #0x0\n\t"
"ADCS %[a], r10, #0x0\n\t"
"ADC %[a], r11, #0x0\n\t"
"ASR %[a], %[a], #31\n\t"
"AND %[a], %[a], #0x13\n\t"
"ADDS r4, r4, %[a]\n\t"
"ADCS r5, r5, #0x0\n\t"
"ADCS r6, r6, #0x0\n\t"
"ADCS r7, r7, #0x0\n\t"
"ADCS r8, r8, #0x0\n\t"
"ADCS r9, r9, #0x0\n\t"
"BFC r11, #31, #1\n\t"
"ADCS r10, r10, #0x0\n\t"
"ADC r11, r11, #0x0\n\t"
"BFC r11, #31, #1\n\t"
"STM %[r], {r4, r5, r6, r7, r8, r9, r10, r11}\n\t"
"MOV r0, #0x0\n\t"
"ADD sp, sp, #0xc0\n\t"