Introduction to Padding Schemes in RSA 관련

The Cryptography Handbook: Exploring RSA PKCSv1.5, OAEP, and PSS

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The RSA algorithm was introduced in 1978 in the seminal paper, ”A Method for Obtaining Digital Signatures and Public-Key Cryptosystems”. Over the decades, as RSA became integral to secure communications, various vulnerabilities and attacks have emerg...

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The Cryptography Handbook: Exploring RSA PKCSv1.5, OAEP, and PSS

The RSA algorithm was introduced in 1978 in the seminal paper, ”A Method for Obtaining Digital Signatures and Public-Key Cryptosystems”. Over the decades, as RSA became integral to secure communications, various vulnerabilities and attacks have emerg...

Before we dive into the padding schemes and how it helps our case, let’s quickly recap the need for padding in RSA.

Textbook RSA encryption is deterministic. The same plaintext always produces the same ciphertext under a given public key. This determinism makes raw RSA insecure. An attacker can guess possible messages, encrypt them with the public key, and compare with the target ciphertext to see which guess matches.

Beyond determinism, small-exponent attacks illustrate why padding is critical. If the message m is too small relative to the modulus, raising it to a small public exponent (like $e=3$) might not wrap around $N$. Padding the plaintext with random data before encryption remedies these problems by making the ciphertext unpredictable and ensuring me spans the modulus’ range.