Implementing Rsa Key Pair Management

Implementing RSA Key Pair Management

Overview

RSA (Rivest-Shamir-Adleman) is the most widely deployed asymmetric cryptographic algorithm, used for digital signatures, key exchange, and encryption. This skill covers generating, storing, rotating, and managing RSA key pairs following NIST SP 800-57 key management guidelines, including key serialization formats (PEM, DER, PKCS#8), passphrase protection, and key strength validation.

When to Use

• When deploying or configuring implementing rsa key pair management capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Common Misconfigurations & Verification

• PKCS#1 v1.5 encryption (padding oracle): RSA/PKCS1v15 decryption that reveals padding-validity (via errors or timing) enables a Bleichenbacher attack to recover plaintext. Use RSA-OAEP (padding.OAEP with SHA-256) for encryption, never PKCS1v15 for new systems.
• PKCS#1 v1.5 signatures: prefer RSA-PSS for signing; if PKCS1v15 verification must stay for legacy, pin the exact hash and never mix.
• Key too small / weak: reject keys <2048 bits (use ≥3072 for new deployments). Validate the modulus bit length and run a weak-key check (small factors, low public exponent like e=3 with no OAEP, shared primes / ROCA).
• Unprotected private key: encrypt private keys with a strong passphrase (BestAvailableEncryption, AES-256) in PKCS#8, and store with 0600 permissions — never commit unencrypted PEMs.
• No key rotation / versioning: rotate at least annually and retain old public keys for verifying historical signatures only.
• Mandatory tests: an RSA-PSS signature over a tampered message is REJECTED; verification with the wrong public key is REJECTED; OAEP decryption of a corrupted ciphertext fails cleanly without leaking padding state; loading the private key with a wrong passphrase fails; key.key_size >= 3072 is asserted.

Prerequisites

• Familiarity with cryptography concepts and tools
• Access to a test or lab environment for safe execution
• Python 3.8+ with required dependencies installed
• Appropriate authorization for any testing activities

Objectives

• Generate RSA key pairs with appropriate key sizes (2048, 3072, 4096 bits)
• Serialize keys in PEM and DER formats with PKCS#8
• Protect private keys with strong passphrase encryption
• Implement key rotation with versioning
• Extract public key components and fingerprints
• Validate key strength and detect weak keys
• Sign and verify data using RSA-PSS

Key Concepts

RSA Key Sizes and Security Strength

RSA Padding Schemes

Key Storage Formats

• PEM: Base64-encoded with headers, human-readable
• DER: Binary ASN.1 encoding, compact
• PKCS#8: Standard for private key encapsulation
• PKCS#12/PFX: Bundled key + certificate, password-protected

Security Considerations

• Minimum 3072-bit keys for new deployments (NIST recommendation)
• Always protect private keys with AES-256-CBC passphrase encryption
• Use RSA-PSS for signatures (not PKCS#1 v1.5)
• Use RSA-OAEP for encryption (not PKCS#1 v1.5)
• Store private keys with restrictive file permissions (0600)
• Implement key rotation at least annually

Validation Criteria

• Key generation produces valid RSA key pair
• Public key can be extracted from private key
• Private key is protected with passphrase
• RSA-PSS signature verification succeeds
• Tampered signature verification fails
• Key fingerprint is computed correctly
• Key rotation maintains old key access for verification