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The attack relies on having a "padding oracle" who freely responds to queries about whether a message is correctly padded or not. The information could be directly given, or leaked through a side-channel. The earliest well-known attack that uses a padding oracle is Bleichenbacher's attack of 1998, which attacks RSA with PKCS #1 v1.5 padding. [1]
The attacker can then combine the oracle with a systematic search of the problem space to complete their attack. [1] The padding oracle attack, and compression oracle attacks such as BREACH, are examples of oracle attacks, as was the practice of "crib-dragging" in the cryptanalysis of the Enigma machine. An oracle need not be 100% accurate ...
The attack uses the padding as an oracle. [4] [5] PKCS #1 was subsequently updated in the release 2.0 and patches were issued to users wishing to continue using the old version of the standard. [3] However, the vulnerable padding scheme remains in use and has resulted in subsequent attacks:
Adaptive-chosen-ciphertext attacks were perhaps considered to be a theoretical concern, but not to have been be manifested in practice, until 1998, when Daniel Bleichenbacher (then of Bell Laboratories) demonstrated a practical attack against systems using RSA encryption in concert with the PKCS#1 v1.5 encoding function, including a version of the Secure Sockets Layer (SSL) protocol used by ...
Koçulu published left-pad on npm, the default package manager for Node.js, a JavaScript runtime environment. [4] [2] Despite its relative obscurity, left-pad was heavily used; the package was used as a dependency by thousands of other software projects and reached over 15 million downloads prior to its removal.
Padding oracle attacks can be avoided by making sure that an attacker cannot gain knowledge about the removal of the padding bytes. This can be accomplished by verifying a message authentication code (MAC) or digital signature before removal of the padding bytes, or by switching to a streaming mode of operation.
While many popular schemes described in standards and in the literature have been shown to be vulnerable to padding oracle attacks, [31] [32] a solution that adds a one-bit and then extends the last block with zero-bits, standardized as "padding method 2" in ISO/IEC 9797-1, [33] has been proven secure against these attacks.
The zero padding in this step is important for step 5. D n = E n−1 XOR P. Exclusive-OR E n−1 with P to create D n. For the first M bits of the block, this is equivalent to CBC mode; the first M bits of the previous block's ciphertext, E n−1, are XORed with the M bits of plaintext of the last plaintext block.