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set random two highest bits

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orignal 2020-01-21 12:18:31 -05:00
parent 0e666e7d6a
commit f497a74ec4
2 changed files with 11 additions and 4 deletions
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13
libi2pd/Elligator.cpp
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@ -1,3 +1,4 @@
#include <openssl/rand.h>
#include "Crypto.h" #include "Crypto.h"
#include "Elligator.h" #include "Elligator.h"
@ -39,8 +40,8 @@ namespace crypto
BN_free (u); BN_free (iu); BN_free (u); BN_free (iu);
} }
bool Elligator2::Encode (const uint8_t * key, uint8_t * encoded, bool highY) const bool Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const
{ {
bool ret = true; bool ret = true;
BN_CTX * ctx = BN_CTX_new (); BN_CTX * ctx = BN_CTX_new ();
BN_CTX_start (ctx); BN_CTX_start (ctx);
@ -61,7 +62,11 @@ namespace crypto
BN_mod_mul (uxxA, uxxA, xA, p, ctx); BN_mod_mul (uxxA, uxxA, xA, p, ctx);
if (Legendre (uxxA, ctx) != -1) if (Legendre (uxxA, ctx) != -1)
{ {
uint8_t randByte; // random highest bits and high y
RAND_bytes (&randByte, 1);
bool highY = randByte & 0x01;
BIGNUM * r = BN_CTX_get (ctx); BIGNUM * r = BN_CTX_get (ctx);
if (highY) if (highY)
{ {
@ -78,6 +83,7 @@ namespace crypto
SquareRoot (r, r, ctx); SquareRoot (r, r, ctx);
bn2buf (r, encoded, 32); bn2buf (r, encoded, 32);
encoded[0] |= (randByte & 0xC0); // copy two highest bits from randByte
for (size_t i = 0; i < 16; i++) // To Little Endian for (size_t i = 0; i < 16; i++) // To Little Endian
{ {
uint8_t tmp = encoded[i]; uint8_t tmp = encoded[i];
@ -105,6 +111,7 @@ namespace crypto
encoded1[i] = encoded[31 - i]; encoded1[i] = encoded[31 - i];
encoded1[31 - i] = encoded[i]; encoded1[31 - i] = encoded[i];
} }
encoded1[0] &= 0x3F; // drop two highest bits
BIGNUM * r = BN_CTX_get (ctx); BN_bin2bn (encoded1, 32, r); BIGNUM * r = BN_CTX_get (ctx); BN_bin2bn (encoded1, 32, r);

2
libi2pd/Elligator.h
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@ -17,7 +17,7 @@ namespace crypto
Elligator2 (); Elligator2 ();
~Elligator2 (); ~Elligator2 ();
bool Encode (const uint8_t * key, uint8_t * encoded, bool highY = false) const; bool Encode (const uint8_t * key, uint8_t * encoded) const;
bool Decode (const uint8_t * encoded, uint8_t * key) const; bool Decode (const uint8_t * encoded, uint8_t * key) const;
private: private: