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93 lines
2.2 KiB
93 lines
2.2 KiB
#include "Crypto.h" |
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#include "Elligator.h" |
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namespace i2p |
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{ |
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namespace crypto |
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{ |
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Elligator2::Elligator2 () |
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{ |
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// TODO: share with Ed22519 |
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p = BN_new (); |
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// 2^255-19 |
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BN_set_bit (p, 255); // 2^255 |
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BN_sub_word (p, 19); |
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p38 = BN_dup (p); BN_add_word (p38, 3); BN_div_word (p38, 8); // (p+3)/8 |
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p12 = BN_dup (p); BN_sub_word (p12, 1); BN_div_word (p12, 2); // (p-1)/2 |
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p14 = BN_dup (p); BN_sub_word (p14, 1); BN_div_word (p14, 4); // (p-1)/4 |
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auto A = BN_new (); BN_set_word (A, 486662); |
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nA = BN_new (); BN_sub (nA, p, A); |
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BN_CTX * ctx = BN_CTX_new (); |
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// calculate sqrt(-1) |
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sqrtn1 = BN_new (); |
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BN_set_word (sqrtn1, 2); |
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BN_mod_exp (sqrtn1, sqrtn1, p14, p, ctx); // 2^((p-1)/4 |
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u = BN_new (); BN_set_word (u, 2); |
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iu = BN_new (); BN_mod_inverse (iu, u, p, ctx); |
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//printf ("%s\n", BN_bn2hex (iu)); |
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BN_CTX_free (ctx); |
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} |
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Elligator2::~Elligator2 () |
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{ |
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BN_free (p); BN_free (p38); BN_free (p12); BN_free (p14); |
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BN_free (sqrtn1); BN_free (A); BN_free (nA); |
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BN_free (u); BN_free (iu); |
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} |
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void Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const |
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{ |
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BN_CTX * ctx = BN_CTX_new (); |
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BN_CTX_start (ctx); |
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BIGNUM * x = BN_CTX_get (ctx); BN_bin2bn (key, 32, x); |
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BIGNUM * xA = BN_CTX_get (ctx); BN_add (xA, x, A); // x + A |
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BN_sub (xA, p, xA); // p - (x + A) |
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BIGNUM * r = BN_CTX_get (ctx); |
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BN_mod_inverse (r, xA, p, ctx); |
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BN_mod_mul (r, r, x, p, ctx); |
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BN_mod_mul (r, r, iu, p, ctx); |
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SquareRoot (r, r, ctx); |
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bn2buf (r, encoded, 32); |
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BN_CTX_end (ctx); |
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BN_CTX_free (ctx); |
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} |
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void Elligator2::SquareRoot (const BIGNUM * x, BIGNUM * r, BN_CTX * ctx) const |
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{ |
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BIGNUM * t = BN_CTX_get (ctx); |
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BN_mod_exp (t, x, p14, p, ctx); // t = x^((p-1)/4) |
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BN_mod_exp (r, x, p38, p, ctx); // r = x^((p+3)/8) |
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BN_add_word (t, 1); |
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if (!BN_cmp (t, p)) |
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BN_mod_mul (r, r, sqrtn1, p, ctx); |
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if (BN_cmp (r, p12) > 0) // r > (p-1)/2 |
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BN_sub (r, p, r); |
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} |
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static std::unique_ptr<Elligator2> g_Elligator; |
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std::unique_ptr<Elligator2>& GetElligator () |
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{ |
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if (!g_Elligator) |
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{ |
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auto el = new Elligator2(); |
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if (!g_Elligator) // make sure it was not created already |
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g_Elligator.reset (el); |
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else |
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delete el; |
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} |
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return g_Elligator; |
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} |
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} |
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} |
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