| /* Copyright lowRISC contributors. */ |
| /* Licensed under the Apache License, Version 2.0, see LICENSE for details. */ |
| /* SPDX-License-Identifier: Apache-2.0 */ |
| |
| /** |
| * Constant time modular multiplication for P-384 based on Solinas reduction |
| * algorithm. |
| */ |
| |
| .section .text |
| |
| /* Initialise WDRs before using them */ |
| bn.xor w14, w14, w14 |
| bn.xor w15, w15, w15 |
| bn.xor w16, w16, w16 |
| |
| /** |
| * Unrolled 768=384x384 bit multiplication. |
| * |
| * Returns c = a x b. |
| * |
| * Flags: Flags have no meaning beyond the scope of this subroutine. |
| * |
| * @param[in] [w9, w8]: a, first operand, max. length 384 bit. |
| * @param[in] [w11, w10]: b, second operand, max. length 384 bit. |
| * @param[in] w31: all-zero. |
| * @param[out] [w16, w15, w14]: c, result, max. length 768 bit. |
| * |
| * Clobbered flag groups: FG0 |
| */ |
| mul384: |
| bn.mulqacc.z w8.0, w10.0, 0 |
| bn.mulqacc w8.0, w10.1, 64 |
| bn.mulqacc.so w14.L, w8.1, w10.0, 64 |
| bn.mulqacc w8.0, w10.2, 0 |
| bn.mulqacc w8.1, w10.1, 0 |
| bn.mulqacc w8.2, w10.0, 0 |
| bn.mulqacc w8.0, w10.3, 64 |
| bn.mulqacc w8.1, w10.2, 64 |
| bn.mulqacc w8.2, w10.1, 64 |
| bn.mulqacc.so w14.U, w8.3, w10.0, 64 |
| bn.mulqacc w8.0, w11.0, 0 |
| bn.mulqacc w8.1, w10.3, 0 |
| bn.mulqacc w8.2, w10.2, 0 |
| bn.mulqacc w8.3, w10.1, 0 |
| bn.mulqacc w9.0, w10.0, 0 |
| bn.mulqacc w8.0, w11.1, 64 |
| bn.mulqacc w8.1, w11.0, 64 |
| bn.mulqacc w8.2, w10.3, 64 |
| bn.mulqacc w8.3, w10.2, 64 |
| bn.mulqacc w9.0, w10.1, 64 |
| bn.mulqacc.so w15.L, w9.1, w10.0, 64 |
| bn.mulqacc w8.1, w11.1, 0 |
| bn.mulqacc w8.2, w11.0, 0 |
| bn.mulqacc w8.3, w10.3, 0 |
| bn.mulqacc w9.0, w10.2, 0 |
| bn.mulqacc w9.1, w10.1, 0 |
| bn.mulqacc w8.2, w11.1, 64 |
| bn.mulqacc w8.3, w11.0, 64 |
| bn.mulqacc w9.0, w10.3, 64 |
| bn.mulqacc.so w15.U, w9.1, w10.2, 64 |
| bn.mulqacc w8.3, w11.1, 0 |
| bn.mulqacc w9.0, w11.0, 0 |
| bn.mulqacc w9.1, w10.3, 0 |
| bn.mulqacc w9.0, w11.1, 64 |
| bn.mulqacc.so w16.L, w9.1, w11.0, 64 |
| bn.mulqacc.so w16.U, w9.1, w11.1, 0 |
| |
| ret |
| |
| /** |
| * Multiplication by the Solinas constant for P-384. |
| * |
| * Returns xK = x * (2^128 + 2^96 - 2^32 + 1) |
| * |
| * For P-384, Solinas reduction involves multiplying by the constant K (K = |
| * 2^384 - modulus). We can efficiently compute the product x * K by expanding |
| * to: |
| * xK = (x << 128) + (x << 96) - (x << 32) + x |
| * |
| * This routine runs in constant time. |
| * |
| * Flags: Flags correspond to the subtraction of (x << 32) from the high limb. |
| * |
| * @param[in] w4 x, input operand |
| * @param[in] w31 all-zero |
| * @param[out] [w7:w6] result |
| * |
| * Clobbered registers: w6, w7 |
| * Clobbered flag groups: FG0 |
| */ |
| mul_k: |
| /* [w7:w6] <= x + (x << 128) */ |
| bn.add w6, w4, w4 << 128 |
| bn.addc w7, w31, w4 >> 128 |
| |
| /* [w7:w6] <= x + (x << 128) + (x << 96) */ |
| bn.add w6, w6, w4 << 96 |
| bn.addc w7, w7, w4 >> 160 |
| |
| /* [w7:w6] <= x + (x << 128) + (x << 96) - (x << 32) = xK */ |
| bn.sub w6, w6, w4 << 32 |
| bn.subb w7, w7, w4 >> 224 |
| |
| ret |
| |
| |
| /** |
| * 384-bit modular multiplication based on Solinas reduction algorithm. |
| * |
| * Returns c = a x b % m. |
| * |
| * Expects the two 384-bit operands a and b to be in "unsaturated" form: rather |
| * than having 256 bits in the first limb and 128 bits in the second, we expect |
| * 192 bits in each limb, so that a = w8 + w9 << 192 and b = w10 + w11 << 192. |
| * The result c is returned in the same format (c = w29 + w30 << 192). |
| * |
| * This routine runs in constant time. |
| * |
| * Flags: Flags have no meaning beyond the scope of this subroutine. |
| * |
| * @param[in] [w9, w8]: a, first operand, max. length 384 bit, a < m. |
| * @param[in] [w11, w10]: b, second operand, max. length 384 bit, b < m. |
| * @param[in] [w13, w12]: m, modulus, max. length 384 bit, 2^384 > m > 2^383. |
| * @param[in] [p384_k]: k, precomputed reduction constant |
| * @param[in] w31: all-zero. |
| * @param[out] [w30, w29]: c, result, max. length 384 bit. |
| * |
| * Clobbered registers: w4 to w7, w14 to w16, w29, w30, acc |
| * Clobbered flag groups: FG0 |
| */ |
| solinas384: |
| /* Compute the raw 768-bit product: |
| ab = [w16:w14] <= a * b */ |
| jal x1, mul384 |
| |
| /* Construct a 256-bit mask that will be useful later on: |
| w30 <= 2^256 - 1 */ |
| bn.not w30, w31 |
| |
| /* Solinas reduction step. Based on the observation that: |
| (x + 2^384 * y) mod (2^384 - K) = (x + K * y) mod (2^384 - K). */ |
| |
| /* Extract the high 128 bits from the middle term and the low 128 bits from |
| the high term, then multiply by K: |
| [w7:w6] <= ab[639:384] * K */ |
| bn.rshi w4, w16, w15 >> 128 |
| jal x1, mul_k |
| |
| /* Isolate the lower 384 bits: |
| w15 <= ab[383:256] */ |
| bn.and w15, w15, w30 >> 128 |
| |
| /* Add product to the lower 384 bits: |
| [w15:w14] = ab[384:0] + (ab[639:384] * K) */ |
| bn.add w14, w14, w6 |
| bn.addc w15, w15, w7 |
| |
| /* Multiply the highest 128 bits of the product by K: |
| [w7:w6] <= ab[767:640] * K */ |
| bn.rshi w4, w31, w16 >> 128 |
| jal x1, mul_k |
| |
| /* Add product to the result to complete the reduction step: |
| [w16:w14] = ab[384:0] + (ab[767:384] * K) */ |
| bn.add w15, w15, w6 |
| bn.addc w16, w31, w7 |
| |
| /* At this point, the intermediate result (henceforth "r") has at most 513 |
| bits (i.e. w16 is at most 1). Start another Solinas reduction step to |
| reduce the bound further. */ |
| |
| /* Multiply the high 129 bits by K: |
| [w7:w6] <= r[512:384] * K */ |
| bn.rshi w4, w16, w15 >> 128 |
| jal x1, mul_k |
| |
| /* Isolate the lower 384 bits: |
| w15 <= r[383:256] */ |
| bn.and w15, w15, w30 >> 128 |
| |
| /* Add product to the lower 384 bits to complete the reduction step: |
| [w15:w14] = r[384:0] + (r[513:384] * K) */ |
| bn.add w14, w14, w6 |
| bn.addc w15, w15, w7 |
| |
| /* At this point, the result is at most 385 bits, and a conditional |
| subtraction is sufficient to fully reduce. */ |
| bn.sub w29, w14, w12 |
| bn.subb w30, w15, w13 |
| |
| /* If the subtraction underflowed (C is set), select the pre-subtraction |
| result; otherwise, select the result of the subtraction. */ |
| bn.sel w29, w14, w29, C |
| bn.sel w30, w15, w30, C |
| |
| /* return result: c =[w29, w30] = a * b % m. */ |
| ret |
| |
| /** |
| * Externally callable wrapper for modular multiplication with |
| * Solinas reduction. |
| * |
| * Returns c = a x b % m. |
| * |
| * @param[in] dmem[first]: a, first operand, max. length 384 bit |
| * @param[in] dmem[second]: b, second operand, max. length 384 bit |
| * @param[in] dmem[modulus]: m, modulus, max. length 384 bit |
| * with 2^384 > m > 2^383 |
| * @param[out] dmem[first]: c, result, max. length 384 bit. |
| */ |
| .section .text.start |
| .globl wrap_solinas384 |
| wrap_solinas384: |
| /* Initialize all-zero register. */ |
| bn.xor w31, w31, w31 |
| /* Initialise WDRs before using them */ |
| bn.xor w14, w14, w14 |
| bn.xor w15, w15, w15 |
| bn.xor w16, w16, w16 |
| /* load first operand from dmem to [w9, w8] */ |
| li x4, 8 |
| la x5, first |
| bn.lid x4++, 0(x5) |
| bn.lid x4++, 32(x5) |
| /* load second operand from dmem to [w11, w10] */ |
| la x5, second |
| bn.lid x4++, 0(x5) |
| bn.lid x4++, 32(x5) |
| /* load modulus from dmem to [w13, w12] */ |
| la x5, modulus |
| bn.lid x4++, 0(x5) |
| bn.lid x4++, 32(x5) |
| |
| jal x1, solinas384 |
| |
| la x5, out |
| li x4, 29 |
| bn.sid x4++, 0(x5) |
| bn.sid x4++, 32(x5) |
| |
| ecall |
| |
| .section .data |
| |
| /* First operand. */ |
| .balign 32 |
| first: |
| .word 0x8f122951 |
| .word 0x73ff314c |
| .word 0x7a097999 |
| .word 0x2051536e |
| .word 0xb64b9530 |
| .word 0xdce2294e |
| .word 0x005c06ab |
| .word 0x95b1756b |
| .word 0x69821679 |
| .word 0x628540cf |
| .word 0x1eb1d98b |
| .word 0x24509793 |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0x00000000 |
| |
| /* Second operand. */ |
| .balign 32 |
| second: |
| .word 0x4d815c86 |
| .word 0x7c37aa39 |
| .word 0x0e92397c |
| .word 0xf6da2fc9 |
| .word 0x617835eb |
| .word 0x52bcdb9c |
| .word 0xbb7f6aaa |
| .word 0xca809d63 |
| .word 0x4c28c407 |
| .word 0x476e9732 |
| .word 0xd0face3d |
| .word 0x922eb7ed |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0x00000000 |
| |
| /* Modulus.*/ |
| .balign 32 |
| modulus: |
| .word 0xffffffff |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0xffffffff |
| .word 0xfffffffe |
| .word 0xffffffff |
| .word 0x00000000 |
| .word 0x00000000 |
| .word 0xffffffff |
| .word 0xffffffff |
| .word 0xffffffff |
| .word 0xffffffff |
| .word 0xffffffff |
| .word 0xffffffff |
| .word 0x00000000 |
| .word 0x00000000 |
| |
| /* Output buffer. */ |
| .balign 32 |
| out: |
| .zero 64 |
| |
| /* |
| Expected result in buffers [w30:w29]: |
| |
| w29 | 0x5054372a_ba0d9ce3_b0d94772_06992345_c7b24eb1_f1fae9f6_2b1edb3d_83a27cdb |
| w30 | 0x00000000_00000000_00000000_00000000_a4fcf2c0_9d974be4_1adb3a1d_d50e68c1 |
| */ |
