SonicOS/X API Reference Guide

RSA Padding

RSA defines two types of padding, the original one specified in PKCS#1 v1.5, and a more recent OAEP padding specified in PKCS#1 v2.0.

PKCS#1 v2.0 utilizes SHA hashing and is more secure and preferred, but gives more size overhead, hence resulting in a smaller maximum password size for a given key size. Refer to Password Size Limits and RSA Key Sizes.

The type of padding to use is configurable, defaulting to OAEP. The client and firewall must be using the same type of padding, and for security it is highly recommended that OAEP padding be used.

OAEP padding uses two hashes (its primary hash and that for its MGF1 mask generation function) and in some versions of SonicOS these too are configurable. In both cases any hashing method that is supported by OpenSSL (the version used in SonicOS) can be used. The two do not need to be the same, but what the client uses in the encryption must match what is configured on the firewall.

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