RSA-2048

In short: RSA with a key length of 2048 bits: a widespread asymmetric algorithm for encryption and signing.

In more detail: RSA (Rivest, Shamir, Adleman, 1977) relies on the fact that large numbers are easy to multiply but hard to factor again. With RSA-2048 the modulus has 2048 bits, about 617 decimal digits.

In Depth

Security

RSA-2048 is considered secure today and corresponds to roughly 112 bits of security. Recommendations (BSI, NIST) advise at least 2048, preferably 3072 bits for new systems. RSA-1024 is considered too weak.

Where it is used

TLS certificates (HTTPS), SSH keys, e-mail signatures and GPG. RSA usually only encrypts a small symmetric key; AES handles the actual data (see hybrid methods).

Limits

RSA is slow compared with symmetric methods. A sufficiently large quantum computer could break RSA using Shor’s algorithm, which is why post-quantum methods are being introduced. Modern alternatives are elliptic curves (ECC) with shorter keys.

See also: Asymmetric Encryption, Public Key, Private Key, AES-256