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kernel: rekey chacha state on each randomread() invocation

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we can encrypt the 256 bit chacha key on each invocation
making it hard to reconstruct previous outputs of the
generator given the current state (backtracking resiatance).
This commit is contained in:
cinap_lenrek 2016-09-11 19:07:17 +02:00
parent 36c9a2489d
commit c0a9c3b551
1 changed files with 2 additions and 1 deletions
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3
sys/src/9/port/random.c
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@ -96,9 +96,10 @@ randomread(void *p, ulong n)
if(hwrandbuf != nil)
(*hwrandbuf)(p, n);
/* copy chacha state and increment iv */
/* copy chacha state, rekey and increment iv */
qlock(rs);
c = *rs;
chacha_encrypt((uchar*)&rs->input[4], 32, &c);
if(++rs->input[13] == 0)
if(++rs->input[14] == 0)
++rs->input[15];