3DES (also “Triple DES”) is an open encryption standard that offers strong encryption at 112-bit and 168-bit strengths.
3DES 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 3DES.)
3DES 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 3DES.)
NIST‘s AES competition was held to find a faster and stronger replacement for 3DES. However, 3DES has not yet been phased out and is expected to remain approved through 2030 for sensitive government information. (Only the 168-bit version is currently allowed; permitted use of the 112-bit version ceased January 1, 2011.) NIST validates specific implementations of 3DES under FIPS 140-2, and several hundred unique implementations have now been validated under that program. The 3DES algorithm itself is specified in FIPS 46-3.
See the Wikipedia entry for 3DES if you are interested in the technical mechanics behind 3DES.
BEST PRACTICE: All modern file transfer clients and file transfer servers should support FIPS-valided AES, FIPS-validated 3DES or both. (AES is faster, may have more longevity and offers higher bit rates; 3DES offers better backwards compatibility.)