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Use constant-time comparison for HMAC signature verification #3997

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Use constant-time comparison for HMAC signature verification #3997

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7 changes: 5 additions & 2 deletions server/src/main/java/org/cloudfoundry/identity/uaa/oauth/jwt/UaaMacSigner.java
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.text.ParseException;
import java.util.Collections;
import java.util.LinkedHashSet;
Expand Down Expand Up @@ -84,8 +85,10 @@ public static JWTClaimsSet verify(String jwToken, JWKSet jwkSet) {
String kid = header.getKeyID();
JWK jwKey = jwkSet.getKeys().stream().filter(e -> kid.equals(e.getKeyID())).findFirst().orElseThrow();
UaaMacSigner internal = new UaaMacSigner((String) jwKey.toJSONObject().get(JWKParameterNames.OCT_KEY_VALUE));
// symmetric signature check: create internal signature and compare if matches the signature from token
if (token.getSignature().equals(internal.sign(header, token.getSigningInput())) && SUPPORTED_ALGORITHMS.contains(header.getAlgorithm())) {
// symmetric signature check: create internal signature and compare if matches the signature from token,
// using a constant-time comparison to avoid leaking timing information about the expected HMAC
Base64URL expectedSignature = internal.sign(header, token.getSigningInput());
if (MessageDigest.isEqual(token.getSignature().decode(), expectedSignature.decode()) && SUPPORTED_ALGORITHMS.contains(header.getAlgorithm())) {
return token.getJWTClaimsSet();
}
throw new InvalidSignatureException("HMAC not mached");
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