diff options
Diffstat (limited to 'comm/third_party/botan/src/lib/math/mp/mp_monty.cpp')
-rw-r--r-- | comm/third_party/botan/src/lib/math/mp/mp_monty.cpp | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp b/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp new file mode 100644 index 0000000000..433d3ff358 --- /dev/null +++ b/comm/third_party/botan/src/lib/math/mp/mp_monty.cpp @@ -0,0 +1,133 @@ +/* +* Montgomery Reduction +* (C) 1999-2011 Jack Lloyd +* 2006 Luca Piccarreta +* 2016 Matthias Gierlings +* +* Botan is released under the Simplified BSD License (see license.txt) +*/ + +#include <botan/internal/mp_core.h> +#include <botan/internal/mp_monty.h> +#include <botan/internal/mp_madd.h> +#include <botan/internal/mp_asmi.h> +#include <botan/internal/ct_utils.h> +#include <botan/mem_ops.h> +#include <botan/exceptn.h> + +namespace Botan { + +namespace { + +/* +* Montgomery reduction - product scanning form +* +* https://www.iacr.org/archive/ches2005/006.pdf +* https://eprint.iacr.org/2013/882.pdf +* https://www.microsoft.com/en-us/research/wp-content/uploads/1996/01/j37acmon.pdf +*/ +void bigint_monty_redc_generic(word z[], size_t z_size, + const word p[], size_t p_size, word p_dash, + word ws[]) + { + word w2 = 0, w1 = 0, w0 = 0; + + w0 = z[0]; + + ws[0] = w0 * p_dash; + + word3_muladd(&w2, &w1, &w0, ws[0], p[0]); + + w0 = w1; + w1 = w2; + w2 = 0; + + for(size_t i = 1; i != p_size; ++i) + { + for(size_t j = 0; j < i; ++j) + { + word3_muladd(&w2, &w1, &w0, ws[j], p[i-j]); + } + + word3_add(&w2, &w1, &w0, z[i]); + + ws[i] = w0 * p_dash; + + word3_muladd(&w2, &w1, &w0, ws[i], p[0]); + + w0 = w1; + w1 = w2; + w2 = 0; + } + + for(size_t i = 0; i != p_size; ++i) + { + for(size_t j = i + 1; j != p_size; ++j) + { + word3_muladd(&w2, &w1, &w0, ws[j], p[p_size + i-j]); + } + + word3_add(&w2, &w1, &w0, z[p_size+i]); + + ws[i] = w0; + w0 = w1; + w1 = w2; + w2 = 0; + } + + word3_add(&w2, &w1, &w0, z[z_size-1]); + + ws[p_size] = w0; + ws[p_size+1] = w1; + + /* + * The result might need to be reduced mod p. To avoid a timing + * channel, always perform the subtraction. If in the compution + * of x - p a borrow is required then x was already < p. + * + * x starts at ws[0] and is p_size+1 bytes long. + * x - p starts at ws[p_size+1] and is also p_size+1 bytes log + * + * Select which address to copy from indexing off of the final + * borrow. + */ + + // word borrow = bigint_sub3(ws + p_size + 1, ws, p_size + 1, p, p_size); + word borrow = 0; + for(size_t i = 0; i != p_size; ++i) + ws[p_size + 1 + i] = word_sub(ws[i], p[i], &borrow); + ws[2*p_size+1] = word_sub(ws[p_size], 0, &borrow); + + BOTAN_DEBUG_ASSERT(borrow == 0 || borrow == 1); + + CT::conditional_copy_mem(borrow, z, ws, ws + (p_size + 1), (p_size + 1)); + clear_mem(z + p_size, z_size - p_size - 2); + } + +} + +void bigint_monty_redc(word z[], + const word p[], size_t p_size, word p_dash, + word ws[], size_t ws_size) + { + const size_t z_size = 2*(p_size+1); + + BOTAN_ARG_CHECK(ws_size >= z_size, "workspace too small"); + + if(p_size == 4) + bigint_monty_redc_4(z, p, p_dash, ws); + else if(p_size == 6) + bigint_monty_redc_6(z, p, p_dash, ws); + else if(p_size == 8) + bigint_monty_redc_8(z, p, p_dash, ws); + else if(p_size == 16) + bigint_monty_redc_16(z, p, p_dash, ws); + else if(p_size == 24) + bigint_monty_redc_24(z, p, p_dash, ws); + else if(p_size == 32) + bigint_monty_redc_32(z, p, p_dash, ws); + else + bigint_monty_redc_generic(z, z_size, p, p_size, p_dash, ws); + } + +} |