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A bit-flipping attack is an attack on a cryptographic cipher in which the attacker can change the ciphertext in such a way as to result in a predictable change of the plaintext, although the attacker is not able to learn the plaintext itself. Note that this type of attack is not—directly—against the cipher itself , but against a particular message or series of messages. In the extreme, this could become a Denial of service attack against all messages on a particular channel using that cipher.
The attack is especially dangerous when the attacker knows the format of the message. In such a situation, the attacker can turn it into a similar message but one in which some important information is altered. For example, a change in the destination address might alter the message route in a way that will force re-encryption with a weaker cipher, thus possibly making it easier for an attacker to decipher the message.
When applied to digital signatures, the attacker might be able to change a promissory note stating "I owe you $10.00" into one stating "I owe you $10,000".
Stream ciphers, such as RC4, are vulnerable to a bit-flipping attack, as are some block cipher modes of operation. See stream cipher attack. A keyed message authentication code, digital signature, or other authentication mechanism allows the recipient to detect if any bits were flipped in transit.