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Dedicate a full r hash block to attacker unknown bytes #1368

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merged 5 commits into from
Nov 9, 2018
Merged

Dedicate a full r hash block to attacker unknown bytes #1368

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70af14b
Dedicate a full r hash block to attacker unknown bytes
PlasmaPower Nov 9, 2018
8226feb
Formatting
rkeene Nov 9, 2018
62e896f
Updated wording
rkeene Nov 9, 2018
08bad94
Updated ranges
rkeene Nov 9, 2018
d31ec86
More words, and better too
rkeene Nov 9, 2018
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10 changes: 9 additions & 1 deletion ed25519-donna/ed25519.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,14 +62,22 @@ ED25519_FN(ed25519_sign) (const unsigned char *m, size_t mlen, const ed25519_sec
ge25519 ALIGN(16) R;
hash_512bits extsk, hashr, hram;
unsigned char randr[32];
static const unsigned char rzero[64] = {0};
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ed25519_extsk(extsk, sk);

/* r = H(aExt[32..64], randr, m) */
/* r = H(aExt[32..63], randr[0..31], zero[0..63], m) */
ed25519_hash_init(&ctx);
ed25519_hash_update(&ctx, extsk + 32, 32);
ed25519_randombytes_unsafe(randr, 32);
ed25519_hash_update(&ctx, randr, 32);
/*
* Pad the rest of the hash block (which is 128
* bytes in size in our case) with zeros.
* This puts the message (possibly known to a side
* channel attacker) in a separate block.
*/
ed25519_hash_update(&ctx, rzero, 64);
ed25519_hash_update(&ctx, m, mlen);
ed25519_hash_final(&ctx, hashr);
expand256_modm(r, hashr, 64);
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