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RSA vs. ECC
To be clear, RSA is still widely used in production and is still considered secure. Where ECC shines is that it is a bit more efficient in terms of both speed and memory usage. Let's take a look at some of the differences between RSA and ECC.
RSA
- RSA key sizes are larger, 2048, 3072, or 4096 bits to remain secure
- RSA's security is based on the difficulty of factoring large numbers
- RSA is relatively slow. Because of this, it is not commonly used to directly encrypt user data. More often, RSA is used to transmit shared keys for symmetric-key cryptography, as it does in TLS/HTTPS.
ECC
- ECC key sizes are smaller, typically 256 bits are enough to remain secure
- ECC's security is based on the mathematics of elliptic curves
Comparing Key Sizes
| Security Bits | RSA (bits) | ECC (bits) |
|---|---|---|
| 80 | 1024 | 160 |
| 112 | 2048 | 224 |
| 128 | 3072 | 256 |
| 192 | 7680 | 384 |
| 256 | 15360 | 512 |
To get 2^256 combinations, RSA requires 15360 bits in a private key, while ECC requires only 512 bits. That's a huge difference! You can save a lot of memory and processing power if you're using a lot of keys. That's why systems like Bitcoin use ECC.