The wrapped key and ciphertext are then sent together to the recipient. Note that in real life we use a hybrid cryptosystem where we encrypt a random symmetric key instead of the message itself, and then proceed to encrypt the message with that random key. This, again, also happens in the PKCS#1 standard (lookup I2OSP which converts an integer to bytes). The usual method for encrypting things with RSA is to use a hybrid mode: you create a random symmetric key (a bunch of random bytes, with a cryptographically secure random number generator), you encrypt symmetrically your data with that key (using a symmetric cipher such as AES), and you encrypt the symmetric key with RSA. A well know mapping of english letters to numeric values is the ASCII character encoding, reproduced below: For example, using the ASCII encoding, HELP would be encoded as 72 - 69 - 76 - 80 - 33. That means that leading zeros should be preserved. In order to use the RSA cryptosystem, it is necessary to use an encoding to represent letters as numbers. After the development of public-key cryptography, the most famous cryptosystem in the world is RSA. Four steps are incorporated in this algorithm: Encryption, Decryption, Key Distribution and Key Generation. This means that you should always use the same number of bytes / hexadecimals to encode the number representing the ciphertext. The letters RSA are the initials of the inventor of the system. This is besides the obvious problem with the RSA key size of course RSA requires specific padding of the input message to be secure.ĭo note though that you will want to distinguish the ciphertext of the letters. ![]() Normally RSA encryption - as specified in the PKCS#1 standards - is randomized, but yours is not, so the same problems of ECB mode persist: identical letters will be encrypted to the same value, which will make it insecure and vulnerable to frequency analysis. Yes, you can actually encrypt using RSA this way, noting though that the resulting ciphertext is malleable (something that can be fixed by digitally signing the plaintext or ciphertext message).
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