The two “PKCS#1 v1.5” are of similar designs, but they are not identical. There are also two common families of digital signature schemes based on RSA, known as PKCS#1 v1.5 and PSS. There are two common families of public-key encryption schemes based on RSA, known as PKCS#1 v1.5 and OAEP. For example, the RSA trapdoor function is based on the difficulty of undoing a multiplication unless you already know one of the factors. Trapdoor functions generally come in families the data necessary to specify one particular element of the family is the public key.Įven though public-key encryption and digital signatures are based on the same concepts, they are not strictly identical. Once again, the magic value required to sign is the private key. If you have a trapdoor function, you can also use it to make a digital signature algorithm: going backward (in the hard direction), the function signs going forward (in the easy direction), the function verifies a signature. The magic value required to decrypt is the private key. If you have a trapdoor function, you can use it to make a public-key encryption algorithm: going forward (in the easy direction), the function encrypts going backward (in the hard direction), the function decrypts. A trapdoor function is like a one-way function, but there is a “magic” value that makes the inverse easy to compute. A one-way function is a function that is easy to compute, but whose inverse is hard to compute. This being said, public-key cryptosystems are based on the concept of trapdoor functions. In general, the public key isn't the right type of mathematical object to use for the decryption algorithm, and the private key isn't the right type of mathematical object to use for the encryption algorithm. This symmetry between public keys and private keys does not extend to most other public-key cryptosystems.
However, the results are not meaningful according to standard algorithms.
(They don't have the same security properties, however - the public key is usually easily guessable from the private key.) You can take an RSA encryption algorithm and feed it a private key, or an RSA decryption algorithm and feed it a public key. With RSA, which is a popular public-key cryptosystem but not the only one, the private key and the public key have the same mathematical properties, so it is possible to use them interchangeably in the algorithms. Similarly, you cannot use a private key to encrypt a message or a public key to decrypt a message. Q: If you pedal backwards on a fish, does it go backwards?Ī fish is not a bicycle.
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