What is padding in RSA encryption?
For example RSA Encryption padding is randomized, ensuring that the same message encrypted multiple times looks different each time. It also avoids other weaknesses, such as encrypting the same message using different RSA keys leaking the message, or an attacker creating messages derived from some other ciphertexts.
How much data can RSA encrypt?
RSA is only able to encrypt data to a maximum amount equal to your key size (2048 bits = 256 bytes), minus any padding and header data (11 bytes for PKCS#1 v1. 5 padding). As a result, it is often not possible to encrypt files with RSA directly (and RSA is not designed for this).
How big of a message can be encrypted with RSA?
Note that the resulting encrypted message length has the same size than the modulus, so the encryption necessarily expands the message size by at least 11 bytes. The normal way of using RSA for encrypted a big message (say, an e-mail) is to use an hybrid scheme:
Is the output of RSA the same as the key size?
So the output of an RSA encryption is the same as the key size: ceil (keySize / 8.0) using floats or (keySize + 8 – 1) / 8 using integers. RSA with OAEP padding uses the same technique, so the answer is correct for OAEP as well (and most other, less known schemes such as RSA-KEM).
Why is padding used for RSA encryption given that it is?
Semantical Security: Add randomness such that RSA is not deterministic anymore (a deterministic encryption scheme yields always the same $x$ for each instance of $x = enc_{pubkey}(m)$ for constant $m$ and $pubkey$). See OAEPas an example on how to achieve this.
What’s the output of the RSA encryption primitive?
The output (as integer) of RSAEP (RSA encryption primitive) is always between 0 and n: If the message representative m is not between 0 and n-1, output message representative out of range and stop.