JARs signed with SHA-1 algorithms are now restricted by default and treated as if they were unsigned. This applies to the algorithms used to digest, sign, and optionally timestamp the JAR. It also applies to the signature and digest algorithms of the certificates in the certificate chain of the code signer and the Timestamp Authority, and any CRLs or OCSP responses that are used to verify if those certificates have been revoked. These restrictions also apply to signed JCE providers.

To reduce the compatibility risk for JARs that have been previously timestamped, there is one exception to this policy:

- Any JAR signed with SHA-1 algorithms and timestamped prior to January 01, 2019 will not be restricted.

This exception may be removed in a future JDK release. To determine if your signed JARs are affected by this change, run `jarsigner -verify -verbose -certs` on the signed JAR, and look for instances of "SHA1" or "SHA-1" and "disabled" and a warning that the JAR will be treated as unsigned in the output.

For example:

```
-  Signed by "CN="Signer""
     Digest algorithm: SHA-1 (disabled)
     Signature algorithm: SHA1withRSA (disabled), 2048-bit key

WARNING: The jar will be treated as unsigned, because it is signed with a weak algorithm that is now disabled by the security property:

  jdk.jar.disabledAlgorithms=MD2, MD5, RSA keySize < 1024, DSA keySize < 1024, SHA1 denyAfter 2019-01-01

```

JARs affected by these new restrictions should be replaced or re-signed with stronger algorithms. 

Users can, *at their own risk*, remove these restrictions by modifying the `java.security` configuration file (or override it by using the `java.security.properties` system property) and removing "SHA1 usage SignedJAR & denyAfter 2019-01-01" from the `jdk.certpath.disabledAlgorithms` security property and "SHA1 denyAfter 2019-01-01" from the `jdk.jar.disabledAlgorithms` security property.