The DES algorithm in Encrypt-Decrypt-Encrypt (EDE) multiple encryption mode, as defined by ANSI X9.17 [6] for encryption and decryption with pairs of 64-bit keys, may be used for DEK and MIC encryption when symmetric key management is employed. The character string "DES-EDE" within an encapsulated a PEM header field indicates use of this algorithm/mode combination.
A compliant PEM implementation supporting symmetric key management may optionally support this algorithm/mode combination.