PKCS #1 Version 1.5 Session Key Retrieval Vulnerability

The data encryption techniques described in RSA's PKCS #1 standard are used in many protocols which rely on, at least in part, the security provided by public-key cryptography systems.

Several protocols which implement the digital enveloping method described in version 1.5 of the PKCS #1 standard are susceptible to an adaptive ciphertext attack which may allow the recovery of session keys, thus compromising the integrity of the data transmitting during that session.

By capturing and logging the packets transmitted between a client and a server, an opponent could make use of a captured encrypted session key to launch a Bleichenbacher attack together with a simple timing attack. If the session key is successfully decrypted, the saved packets can easily be decrypted in a uniform manner.

Interactive key establishment protocols, such as SSH or SSL, are generally significantly more susceptible to successful attacks.


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