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use SecureRandom for digest auth cnonce #2220

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use SecureRandom for digest auth cnonce #2220

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7 changes: 5 additions & 2 deletions client/src/main/java/org/asynchttpclient/Realm.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,9 @@

import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Map;
import java.util.concurrent.ThreadLocalRandom;

import static java.nio.charset.StandardCharsets.ISO_8859_1;
import static java.nio.charset.StandardCharsets.UTF_8;
Expand Down Expand Up @@ -283,6 +283,9 @@ public enum AuthScheme {
*/
public static class Builder {

// cnonce must be unpredictable (RFC 7616 section 3.3), like the NTLM and SCRAM nonces
private static final SecureRandom CNONCE_RANDOM = new SecureRandom();

@hyperxpro hyperxpro Jul 1, 2026

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Don't share one static SecureRandom; use a ThreadLocal. newCnonce runs on Netty event-loop threads (digest header build + 401/407 interceptors), and SecureRandom#nextBytes locks internally, so a single shared instance makes all event loops queue on one lock. ThreadLocalRandom had no such lock. ScramEngine already handles this the right way:

private static final ThreadLocal<SecureRandom> CNONCE_RANDOM = ThreadLocal.withInitial(SecureRandom::new);

and in newCnonce:

CNONCE_RANDOM.get().nextBytes(b);


private final @Nullable String principal;
private final @Nullable String password;
private @Nullable AuthScheme scheme;
Expand Down Expand Up @@ -610,7 +613,7 @@ public Builder parseProxyAuthenticateHeader(String headerLine) {

private void newCnonce(MessageDigest md) {
byte[] b = new byte[8];
ThreadLocalRandom.current().nextBytes(b);
CNONCE_RANDOM.nextBytes(b);
byte[] full = md.digest(b);

@hyperxpro hyperxpro Jul 1, 2026

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the md.digest(b) step is now pointless. The 8 bytes are already cryptographically random, so hashing them and trimming back to 8 bytes adds nothing. The method can just be:

private void newCnonce() {
    byte[] b = new byte[8];
    CNONCE_RANDOM.get().nextBytes(b);
    cnonce = toHexString(b);
}

Same 16-hex-char cnonce. This is safe because pooledMessageDigest already resets the digest before build() gets it, so nothing downstream depends on the digest(b) call.

// trim to first 8 bytes → 16 hex chars
byte[] small = Arrays.copyOf(full, Math.min(8, full.length));
Expand Down
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