Original: However, this option is susceptible to certain chosen-plaintext or known-plaintext attacksRalph Merkle, Martin Hellman: On the Security of Multiple Encryption (PDF), Communications of the ACM, Vol 24, No 7, pp 465–467, July 1981.
Simplified: However, this mode is susceptible to certain chosen-plaintext or known-plaintext attacks Ralph Merkle, Martin Hellman: On the Security of Multiple Encryption (PDF), Communications of the ACM, Vol 24, No 7, pp 465–467, July 1981.