RSA keys should be at least 2,048 bits

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Metadata

ID: rust-security/rsa-key-too-short

Language: Rust

Severity: Warning

Category: Security

CWE: 326

Related CWEs:

Description

RSA keys shorter than 2,048 bits can be factored with modern hardware and cloud-scale compute, exposing encrypted data and signatures to recovery or forgery. NIST SP 800-57 recommends a minimum of 2,048 bits, with 3,072 or 4,096 bits preferred for data with long-term secrecy requirements. The min-length argument can be raised above the 2,048-bit default to enforce a stricter threshold. Values below 2,048 are clamped to the NIST minimum.

Learn More

CWE-326: Inadequate Encryption Strength

Arguments

min-length: Minimum length of the RSA key. Default: 2048.

Non-Compliant Code Examples

use rsa::RsaPrivateKey;
use openssl::rsa::Rsa;
use rand::rngs::OsRng;

fn bad() -> Result<(), Box<dyn std::error::Error>> {
    let mut rng = OsRng;

    // `rsa` crate — classic too-short key
    let _ = RsaPrivateKey::new(&mut rng, 1024)?;

    // Fully qualified path
    let _ = rsa::RsaPrivateKey::new(&mut rng, 1024)?;

    // Digit separator below threshold
    let _ = RsaPrivateKey::new(&mut rng, 1_024)?;

    // Type-suffixed literal below threshold
    let _ = RsaPrivateKey::new(&mut rng, 1024usize)?;

    // new_with_exp also flagged
    let exp = rsa::BoxedUint::from(65537u64);
    let _ = rsa::RsaPrivateKey::new_with_exp(&mut rng, 1024, exp)?;

    // `openssl` crate
    let _ = Rsa::generate(1024)?;

    Ok(())
}

Compliant Code Examples

use rsa::RsaPrivateKey;
use openssl::rsa::Rsa;
use rand::rngs::OsRng;

fn ok() -> Result<(), Box<dyn std::error::Error>> {
    let mut rng = OsRng;

    // `rsa` crate at the minimum
    let _ = RsaPrivateKey::new(&mut rng, 2048)?;

    // Digit separator and type suffix — both >= 2048
    let _ = RsaPrivateKey::new(&mut rng, 2_048)?;
    let _ = RsaPrivateKey::new(&mut rng, 4096usize)?;

    // Fully qualified path
    let _ = rsa::RsaPrivateKey::new(&mut rng, 2048)?;

    // new_with_exp with sufficient bits
    let exp = rsa::BoxedUint::from(65537u64);
    let _ = rsa::RsaPrivateKey::new_with_exp(&mut rng, 2048, exp)?;

    // `openssl` crate at or above the minimum
    let _ = Rsa::generate(2048)?;
    let _ = openssl::rsa::Rsa::generate(4096)?;

    Ok(())
}