| Name |
Padding Oracle Crypto Attack |
|
| Likelyhood of attack |
Typical severity |
| High |
High |
|
| Summary |
An adversary is able to efficiently decrypt data without knowing the decryption key if a target system leaks data on whether or not a padding error happened while decrypting the ciphertext. A target system that leaks this type of information becomes the padding oracle and an adversary is able to make use of that oracle to efficiently decrypt data without knowing the decryption key by issuing on average 128*b calls to the padding oracle (where b is the number of bytes in the ciphertext block). In addition to performing decryption, an adversary is also able to produce valid ciphertexts (i.e., perform encryption) by using the padding oracle, all without knowing the encryption key. |
| Prerequisites |
The decryption routine does not properly authenticate the message / does not verify its integrity prior to performing the decryption operation The target system leaks data (in some way) on whether a padding error has occurred when attempting to decrypt the ciphertext. The padding oracle remains available for enough time / for as many requests as needed for the adversary to decrypt the ciphertext. |
| Solutions | Design: Use a message authentication code (MAC) or another mechanism to perform verification of message authenticity / integrity prior to decryption Implementation: Do not leak information back to the user as to any cryptography (e.g., padding) encountered during decryption. |
| Related Weaknesses |
|
CWE ID
|
Description
|
| CWE-209 |
Generation of Error Message Containing Sensitive Information |
| CWE-347 |
Improper Verification of Cryptographic Signature |
| CWE-354 |
Improper Validation of Integrity Check Value |
| CWE-514 |
Covert Channel |
| CWE-649 |
Reliance on Obfuscation or Encryption of Security-Relevant Inputs without Integrity Checking |
| CWE-696 |
Incorrect Behavior Order |
|
| Related CAPECS |
|
CAPEC ID
|
Description
|
| CAPEC-97 |
Cryptanalysis is a process of finding weaknesses in cryptographic algorithms and using these weaknesses to decipher the ciphertext without knowing the secret key (instance deduction). Sometimes the weakness is not in the cryptographic algorithm itself, but rather in how it is applied that makes cryptanalysis successful. An attacker may have other goals as well, such as: Total Break (finding the secret key), Global Deduction (finding a functionally equivalent algorithm for encryption and decryption that does not require knowledge of the secret key), Information Deduction (gaining some information about plaintexts or ciphertexts that was not previously known) and Distinguishing Algorithm (the attacker has the ability to distinguish the output of the encryption (ciphertext) from a random permutation of bits). |
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