compare X-Sttc-Token in constant time - #250
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PsHeader.auth used String#equals to check the supplied token against the stored user token. String#equals short-circuits on the first mismatching character, so the response latency of the auth path leaks the token byte by byte to a network attacker. Replace the comparison with MessageDigest.isEqual over UTF-8 bytes so the check runs in time proportional to the longer input regardless of where the mismatch falls. Closes sttc#248
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PsHeader.authchecked the suppliedX-Sttc-Tokenheader against the stored user token withString#equals, which short-circuits at the first mismatching character and lets a network attacker recover the secret byte by byte by measuring response latency. The token is the only credential a non-cookie client presents, so the timing leak compromises every counter, lock, and quota of the affected account.After this change the comparison runs through
MessageDigest.isEqualover the UTF-8 bytes of both strings, so the wall-clock cost of the check no longer depends on where the mismatch falls. Header-based authentication continues to reject mismatched tokens with HTTP 401 and to admit matching ones with the sameIdentity.Simpleit produced before.Locally I ran
mvn --batch-mode install -Pqulice -Dmaven.test.skip=true(BUILD SUCCESS) andmvn --batch-mode test -Dtest=TkAppAuthTest(3 tests passed, 0 failed). The widermvn testrun hits pre-existing errors inRsPageTest,TkCountersTest,TkErrorTest,TkHomeTest,TkLocksTest, and theDy*ITCaseintegration tests, all of which fail identically onmasterbefore this branch.Closes #248