Daniel Bleichenbacher (born 1964) is a Swiss cryptographer, previously a researcher at Bell Labs, Google, and Cure53.
He received his Ph.D. from ETH Zurich in 1996 for contributions to computational number theory, particularly concerning message verification in the ElGamal and RSA public-key cryptosystems.
These attacks were able to break both RSA encryption and signatures produced using the PKCS #1 standard.
In 1998, Daniel Bleichenbacher demonstrated a practical attack against systems using RSA encryption in concert with the PKCS #1 encoding function, including a version of the Secure Sockets Layer (SSL) protocol used by thousands of web servers at the time.
In 2006 at a rump session at CRYPTO, Bleichenbacher described a "pencil and paper"-simple attack against RSA signature validation as implemented in common cryptographic toolkits.