What is RSA Encryption?
RSA (Rivest–Shamir–Adleman) is a widely used asymmetric encryption algorithm. Unlike symmetric encryption, RSA uses a pair of keys: a public key for encryption and a private key for decryption. It's a foundational technology for securing digital communications, especially over the internet.
Key Features of RSA
Asymmetric Encryption
Uses two keys — public and private.
Based on Number Theory
Relies on the difficulty of factoring large prime numbers.
Key Lengths
Commonly 2048 or 4096 bits.
Slower
Not ideal for bulk data encryption.
Common Uses
Secure Key Exchange
Exchanging symmetric keys securely.
Digital Signatures
Verifying authenticity and integrity of data.
SSL/TLS (HTTPS)
Securing web communications.
Email Encryption
Securing email content (e.g., PGP, S/MIME).
How RSA Works
RSA uses a pair of mathematically linked keys. Here’s a simplified view of the process:
- Generate two large prime numbers (p and q).
- Compute
n = p × qandϕ(n) = (p - 1)(q - 1). - Choose public exponent
esuch that 1 < e < ϕ(n). - Calculate private exponent
dsuch thatd × e ≡ 1 (mod ϕ(n)). - Publish
{e, n}as the public key and keep{d, n}private.
To encrypt, the sender uses the recipient’s public key. To decrypt, the recipient uses their private key.
Encryption vs. Signing
- Encrypt with the recipient's public key
- Decrypt with the recipient's private key
- Used for confidentiality.
- Sign with your private key
- Verify with your public key
- Used for authenticity and integrity.
Limitations of RSA
- Slower than symmetric algorithms like AES.
- Not suitable for encrypting large files directly.
- Quantum computers could eventually break RSA.
RSA vs Symmetric Encryption
| Feature | RSA | AES |
|---|---|---|
| Type | Asymmetric | Symmetric |
| Keys Used | Public & Private | Single Shared Key |
| Speed | 🐢 Slow | ⚡ Fast |
| Best For | Key exchange, signatures | Bulk data encryption |
| Security Basis | Prime factorization | Substitution & permutation |