What is AES?
AES (“Advanced Encryption Standard”) is an open encryption standard that offers fast encryption at 128-bit, 192-bit and 256-bit strengths.
AES is a symmetric encryption algorithm often used today to secure data in motion in both SSH and SSL/TLS. (After asymmetric key exchange is used perform the handshake in a SSH or SSL/TLS sessions, data is actually transmitted using a symmetric algorithm such as AES.)
AES is also often used today to secure data at rest in SMIME, PGP, AS2, strong Zip encryption and many vendor-specific implementations. (After asymmetric key exchange is used to unlock a key on data at rest, data is actually read or written using a symmetric algorithm such as AES.)
Rijndael is what AES was called before 2001. In that year, NIST selected Rijndael as the new AES algorithm and Rinjdahl became known as AES. NIST validates specific implementations of AES under FIPS 140-2, and several hundred unique implementations have now been validated under that program.
See the Wikipedia entry for AES if you are interested in the technical mechanics behind AES.
BEST PRACTICE: All modern file transfer clients and file transfer servers should support FIPS-validated AES, FIPS-validated 3DES or both. (AES is faster, may have more longevity and offers higher bit rates; 3DES offers better backwards compatibility.)