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Use constant-time comparison for the JWE auth tag and the OIDC at_hash claim #411

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Use constant-time comparison for the JWE auth tag and the OIDC at_hash claim #411

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3 changes: 2 additions & 1 deletion jose/jwe.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import binascii
import hmac
import json
import zlib
from collections.abc import Mapping
Expand Down Expand Up @@ -244,7 +245,7 @@ def _decrypt_and_auth(cek_bytes, enc, cipher_text, iv, aad, auth_tag):
raise NotImplementedError(f"enc {enc} is not implemented!")

plaintext = encryption_key.decrypt(cipher_text, iv, aad, auth_tag)
if auth_tag != auth_tag_check:
if not hmac.compare_digest(auth_tag, auth_tag_check):
raise JWEError("Invalid JWE Auth Tag")

return plaintext
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4 changes: 3 additions & 1 deletion jose/jwt.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import hmac
import json
from calendar import timegm
from datetime import datetime, timedelta
Expand Down Expand Up @@ -468,7 +469,8 @@ def _validate_at_hash(claims, access_token, algorithm):
msg = "Unable to calculate at_hash to verify against token claims."
raise JWTClaimsError(msg)

if claims["at_hash"] != expected_hash:
at_hash = claims["at_hash"]
if not isinstance(at_hash, str) or not hmac.compare_digest(at_hash, expected_hash):
raise JWTClaimsError("at_hash claim does not match access_token.")


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