cryptography Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...

, blinding first became known in the context of blind signatures, where the message author ''blinds'' the message with a random ''blinding factor'', the signer then signs it and the message author "''unblinds"'' it'';'' signer and message author are different parties. Since the late 1990s, blinding mostly refer to countermeasures against

side-channel attacks In computer security, a side-channel attack is a type of security exploit that leverages information inadvertently leaked by a system—such as timing, power consumption, or electromagnetic or acoustic emissions—to gain unauthorized access to ...

on encryption devices, where the random ''blinding'' and the "''unblinding"'' happen on the encryption devices. Blinding must be applied with care, for example Rabin–Williams signatures. If blinding is applied to the formatted message but the random value does not honor Jacobi requirements on ''p'' and ''q'', then it could lead to private key recovery. A demonstration of the recovery can be seen in "Common Vulnerabilities and Exposures" discovered by Evgeny Sidorov. The

one-time pad The one-time pad (OTP) is an encryption technique that cannot be Cryptanalysis, cracked in cryptography. It requires the use of a single-use pre-shared key that is larger than or equal to the size of the message being sent. In this technique, ...

(OTP) is an application of blinding to the secure communication problem, by its very nature. Alice would like to send a message to Bob secretly, however all of their communication can be read by Oscar. Therefore, Alice sends the message after blinding it with a secret key or OTP that she shares with Bob. Bob reverses the blinding after receiving the message. In this example, both blinding and its reversal typically use the XOR operation. Blinding can also be used to prevent certain

side-channel attack In computer security, a side-channel attack is a type of security exploit that leverages information inadvertently leaked by a system—such as timing, power consumption, or electromagnetic or acoustic emissions—to gain unauthorized access to ...

s on asymmetric encryption schemes. Side-channel attacks allow an adversary to recover information about the input to a cryptographic operation, by measuring something other than the algorithm's result, e.g., power consumption, computation time, or radio-frequency emanations by a device. Typically these attacks depend on the attacker knowing the characteristics of the algorithm, as well as (some) inputs. In this setting, blinding serves to alter the algorithm's input into some unpredictable state. Depending on the characteristics of the blinding function, this can prevent some or all leakage of useful information. Note that security depends also on the resistance of the blinding functions themselves to side-channel attacks.

Examples

* In RSA blinding involves computing the blinding operation , where ''r'' is a random integer between 1 and ''N'' and

relatively prime In number theory, two integers and are coprime, relatively prime or mutually prime if the only positive integer that is a divisor of both of them is 1. Consequently, any prime number that divides does not divide , and vice versa. This is equiv ...

to ''N'' (i.e. , ''x'' is the plaintext, ''e'' is the public RSA exponent and ''N'' is the RSA modulus. As usual, the decryption function is applied thus giving . Finally it is unblinded using the function . Multiplying by yields , as desired. When decrypting in this manner, an adversary who is able to measure time taken by this operation would not be able to make use of this information (by applying timing attacks RSA is known to be vulnerable to) as she does not know the constant ''r'' and hence has no knowledge of the real input fed to the RSA primitives.
Blinding in GPG 1.x

References

External links

Breaking the Rabin-Williams digital signature system implementation in the Crypto++ library
{{DEFAULTSORT:Blinding (Cryptography) Cryptography