What is a Java Keystore file? I heard that it used to provide CA certificates to Java applications.

A Java Keystore file is a specially formatted file used to store cryptographic keys and certificates.

A Java KeyStore file can be used to store 3 types of entries:

1. PrivateKeyEntry - This type of entry holds a cryptographic Private Key, which is optionally stored in a protected format to prevent unauthorized access. It is also accompanied by a certificate chain for the corresponding public key.

Private keys and certificate chains are used by a given entity for self-authentication. Applications for this authentication include software distribution organizations which sign JAR files as part of releasing and/or licensing software.

2. SecretKeyEntry - This type of entry holds a cryptographic Secret Key, which is optionally stored in a protected format to prevent unauthorized access.

This type of entry can be used to do symmetric-key encryption, where the recipient of the encrypted message needs to use the same secret key to decrypt the message.

3. TrustedCertificateEntry - This type of entry contains a single public key Certificate belonging to another party. It is called a trusted certificate because the keystore owner trusts that the public key in the certificate indeed belongs to the identity identified by the subject (owner) of the certificate.

This type of entry can be used to authenticate other parties.

Java KeyStore files can be managed by the Java "keytool" program.