Final answer:
The NSA-approved cryptographic algorithm that is not registered with the Federal Info Processing Center is the TwoFish algorithm.
Step-by-step explanation:
The NSA (National Security Agency) approved cryptographic algorithms are those considered suitable for protecting classified information. There are several cryptographic algorithms that are approved by the NSA but are not registered with the Federal Info Processing Center (FIPS). One example is the TwoFish algorithm, which is a symmetric key block cipher algorithm that was a finalist in the Advanced Encryption Standard (AES) competition.