Network Security News

Data encryption security flaw found in 'bullet-proof' SSH protocol

Wednesday, May 20, 2009

Security researchers have uncovered a flaw in the encryption protocol Open Secure Shell (OpenSSH), which was previously thought to provide a "bullet-proof" channel between networked devices.

Researcher Kenny Paterson from the Royal Holloway, University of London, revealed the flaw last November, but did not disclose the full findings until this week at the IEEE Symposium on Security and Privacy in Oakland.

Paterson and his team discovered a basic data security design flaw which, if exploited, could potentially allow an attacker to recover up to 32 bits of plaintext from an arbitrary block of ciphertext from a connection secured using the SSH protocol in the standard configuration.

Paterson told CNET news that a man-in-the-middle attacker could grab blocks of encrypted text as they are sent from client to server and then retransmit the data to the server until the connection was stopped.

The attacker could count out how many bytes it takes until the server stops the connection and then deduce what was in the OpenSSH encryption field before encryption, CNET reported.

"While the attacks have low success probabilities, it should be kept in mind that SSH is regarded as being a bullet-proof protocol and is widely used to protect remote logins to sensitive systems," Paterson said, according to a report from the university.