RSAd

RSAd is a hypothetical RSA-based digital signature algorithm designed for producing and verifying digital signatures. In this scheme, the signer holds a private exponent d and a public exponent e, together with the modulus n, forming the RSA key pair. The core idea is to sign a message by applying a mathematical operation involving the private key, and then allow a recipient to verify the signature using the public key.

In a typical RSAd workflow, a message m is first mapped to a fixed-size digest using a cryptographic hash function H. The signature is computed as s = H(m)^d mod n. Verification checks that H(m) ≡ s^e mod n, confirming that the signer possessed the corresponding private key without revealing it. To achieve security against chosen-message attacks and other weaknesses, RSAd implementations employ padding schemes such as RSA-PSS or PKCS #1 v1.5, which encode the hash in a randomized or structured way before signing.

Security considerations for RSAd hinge on the hardness of factoring the modulus n and the strength of the padding and hash functions. Modern practice typically requires large moduli (2048 bits or more) and careful attention to side-channel resistance in implementations. RSAd must also be kept up to date with current standards for hashing and padding to remain resilient against advances in cryptanalysis.

Applications of RSAd include digital signatures for software code, documents, and secure communications, where authentication of the signer and integrity of the content are essential. RSAd is distinguished from RSA encryption by its primary role in authentication and non-repudiation rather than confidentiality. See also RSA, digital signature, PKCS #1, RSA-PSS.