Hello,

With the keytool command one can generate an ML-KEM key pair and sign the certificate with an EC key (similar to https://openjdk.org/jeps/496):

echo "Creating SERVER keypair"
keytool -genkeypair \
  -alias $SERVER_ALIAS \
  -keyalg ec \
  -dname "CN=localhost, OU=Dev, O=MyOrg, L=City, ST=State, C=US" \
  -validity 365 \
  -keystore server.p12 \
  -storetype PKCS12 \
  -storepass $PASSWORD \
  -keypass $PASSWORD

keytool -keystore server.p12 \
  -storepass $PASSWORD \
  -genkeypair -alias server-mlkem \
  -keyalg ML-KEM-768 \
  -dname "CN=localhost, OU=Dev, O=MyOrg, L=City, ST=State, C=US" \
  -signer $SERVER_ALIAS

When monitoring for X509 certificate details via `jdk.X509Certificate`, I've registered the following event for the ML-KEM key, mentioning that the keyLength is -1:

jdk.X509Certificate {
  startTime = 10:40:10.001 (2025-06-04)
  algorithm = "SHA384withECDSA"
  serialNumber = "2c:37:78:b9:15:08:56:97"
  subject = "CN=localhost, OU=Dev, O=MyOrg, L=City, ST=State, C=US"
  issuer = "CN=localhost, OU=Dev, O=MyOrg, L=City, ST=State, C=US"
  keyType = "ML-KEM"
  keyLength = -1
  certificateId = 3999547851
  validFrom = 14:37:39.000 (2025-06-03)
  validUntil = 14:37:39.000 (2025-09-01)
  eventThread = "main" (javaThreadId = 3)
  stackTrace = [
    sun.security.jca.JCAUtil.tryCommitCertEvent(Certificate) line: 128
    java.security.cert.CertificateFactory.generateCertificate(InputStream) line: 360
    sun.security.pkcs12.PKCS12KeyStore.loadSafeContents(DerInputStream) line: 2406
    sun.security.pkcs12.PKCS12KeyStore.lambda$engineLoad$0(AlgorithmParameters, byte[], char[]) line: 2105
    sun.security.pkcs12.PKCS12KeyStore$RetryWithZero.run(PKCS12KeyStore$RetryWithZero, char[]) line: 254
  ]
}

The key length of an asymmetric key refers to the size of its modulus, but post-quantum algorithms based on lattice cryptography, such as ML-KEM, do not use a modulus. Instead NIST assigns a security category to each standardized parameter set: for example, ML-KEM-768 is assigned to category 3, and ML-DSA-87 to category 5. So the -1 value seems to stand for "Not Available" in this case, but maybe a better solution or documentation would explain how JFR captures details when post-quantum cryptography algorithms are used.