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Fix for issue #356 HKDF infinite loop bug for n = 255 #361

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Merged
merged 3 commits into from
May 10, 2019
Merged

Fix for issue #356 HKDF infinite loop bug for n = 255 #361

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b2b5ff6
Fix for issue #356 HKDF infinite loop bug for n = 255
ttjsu-aws May 8, 2019
0689279
Changed pointer casting to integer cast and unsigned int to uint32_t …
ttjsu-aws May 9, 2019
70729a6
Naming is hard. Updated variable names from PR suggestion
ttjsu-aws May 10, 2019
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6 changes: 3 additions & 3 deletions source/hkdf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -77,14 +77,14 @@ static int aws_cryptosdk_hkdf_expand(
if (!prk || !okm->len || !prk_len) goto err;
n = (okm->len + hash_len - 1) / hash_len;
if (n > 255) goto err;

for (uint8_t idx = 1; idx <= n; idx++) {
for (uint32_t idx = 1; idx <= n; idx++) {
uint8_t idx_byte = idx;
if (!HMAC_Init_ex(&ctx, prk, prk_len, evp_md, NULL)) goto err;
if (idx != 1) {
if (!HMAC_Update(&ctx, t, hash_len)) goto err;
}
if (!HMAC_Update(&ctx, info->buffer, info->len)) goto err;
if (!HMAC_Update(&ctx, &idx, 1)) goto err;
if (!HMAC_Update(&ctx, &idx_byte, 1)) goto err;
if (!HMAC_Final(&ctx, t, &t_len)) goto err;

assert(t_len == hash_len);
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