With one exception, keytool will always print a warning if the certificate, certificate request, or CRL it is parsing, verifying, or generating is using a weak algorithm or key. When a certificate is from an existing `TrustedCertificateEntry`, either in the keystore directly operated on or in the `cacerts` keystore when the `-trustcacerts` option is specified for the `-importcert` command, keytool will not print a warning if it is signed with a weak signature algorithm. For example, suppose the file `cert` contains a CA certificate signed with a weak signature algorithm, `keytool -printcert -file cert` and `keytool -importcert -file cert -alias ca -keystore ks` will print out a warning, but after the last command imports it into the keystore, `keytool -list -alias ca -keystore ks` will not show a warning anymore.

An algorithm or a key is weak if it matches the value of the `jdk.certpath.disabledAlgorithms` security property defined in the `conf/security/java.security` file.