This field specifies the algorithm used by the issuer to sign the certificate, and any parameters associated with the algorithm. (The certificate signature is appended to the data structure, as defined by the signature macro in X.509. This algorithm identification information is replicated with the signature.) The signature is validated by the UA processing a certificate, in order to determine that the integrity of its contents have not been modified subsequent to signing by a CA (IPRA, or PCA). In this context, a signature is effected through the use of a Certificate Integrity Check (CIC) algorithm and a public-key encryption algorithm. RFC 1423 contains the definitions and algorithm IDs for signature algorithms employed in this architecture.