OUD 12c - How to Customize the Size of Ephemeral Diffie-Hellman Keys (Doc ID 2606315.1)

Last updated on MAY 09, 2023

Applies to:

Goal

From Customizing Size of Ephemeral Diffie-Hellman Keys -

Diffie-Hellman (DH) keys of sizes less than 1024 bits have been deprecated because of their insufficient strength. In JDK 8, you can customize the ephemeral DH key size with the system property jdk.tls.ephemeralDHKeySize. This system property does not impact DH key sizes in ServerKeyExchange messages for exportable cipher suites. It impacts only the DHE_RSA, DHE_DSS, and DH_anon-based cipher suites in the JSSE Oracle provider.

You can specify one of the following values for this property:

• Undefined: A DH key of size 1024 bits will be used always for non-exportable cipher suites. This is the default value for this property.
• legacy: The JSSE Oracle provider preserves the legacy behavior (for example, using ephemeral DH keys of sizes 512 bits and 768 bits) of JDK 7 and earlier releases.
• matched: For non-exportable anonymous cipher suites, the DH key size in ServerKeyExchange messages is 1024 bits. For X.509 certificate based authentication (of non-exportable cipher suites), the DH key size matching the corresponding authentication key is used, except that the size must be between 1024 bits and 2048 bits. For example, if the public key size of an authentication certificate is 2048 bits, then the ephemeral DH key size should be 2048 bits unless the cipher suite is exportable. This key sizing scheme keeps the cryptographic strength consistent between authentication keys and key-exchange keys.
• A valid integer between 1024 and 2048, inclusively: A fixed ephemeral DH key size of the specified value, in bits, will be used for non-exportable cipher suites.

Solution

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