Asymmetric Encryption
debt(d5/e5/b5/t7)
Closest to 'specialist tool catches' (d5), semgrep rules can flag openssl_public_encrypt with PKCS1 padding or RSA used for bulk data, but it requires a security-focused tool, not a default linter.
Closest to 'touches multiple files / significant refactor' (e5), swapping padding mode is one line (quick_fix), but moving from raw RSA to hybrid encryption (RSA-wrap AES key + AES-encrypt data) requires restructuring the encryption layer across multiple call sites.
Closest to 'persistent productivity tax' (b5), crypto choices applied across web/cli contexts shape key management, certificate handling, and rotation policies for many work streams; not architecture-defining but a sustained tax.
Closest to 'serious trap' (t7), the misconception that asymmetric is simply 'better' than symmetric, plus the encryption-vs-signing key-direction confusion and the silent Bleichenbacher vulnerability in default PKCS1 padding, all contradict naive intuition.
Also Known As
TL;DR
Explanation
RSA and ECC (Elliptic Curve Cryptography) are the dominant asymmetric systems. The public key encrypts or verifies; the private key decrypts or signs. Asymmetric encryption solves the key distribution problem — you can share your public key openly. However, it is 100-1000× slower than symmetric encryption, so in practice it is used to encrypt a symmetric session key (hybrid encryption), which then encrypts the actual data. TLS uses this hybrid approach.
Diagram
flowchart LR
subgraph Key_Generation
PRIV[Private Key<br/>kept secret]
PUB[Public Key<br/>shared freely]
PRIV -.->|mathematically linked| PUB
end
subgraph Encryption
PLAIN[Plaintext] -->|encrypt with PUBLIC key| CIPHER[Ciphertext]
CIPHER -->|decrypt with PRIVATE key| PLAIN2[Plaintext]
end
subgraph Signing
MSG[Message] -->|sign with PRIVATE key| SIG[Signature]
SIG -->|verify with PUBLIC key| VALID[Valid or Invalid]
end
style PRIV fill:#f85149,color:#fff
style PUB fill:#238636,color:#fff
style CIPHER fill:#6e40c9,color:#fff
style VALID fill:#238636,color:#fff
Common Misconception
Why It Matters
Common Mistakes
- Encrypting large data directly with RSA — RSA is limited to key size minus padding; use hybrid encryption for bulk data.
- Using RSA 1024 — considered broken; use RSA 4096 or prefer Ed25519 for new systems.
- Confusing encryption (public key encrypts, private decrypts) with signing (private key signs, public verifies).
- Not verifying the certificate chain — public keys must be trusted via PKI; a bare public key with no chain verification is not secure.
Code Examples
// RSA encryption of large data — will fail or be insecure:
$data = file_get_contents('largefile.pdf'); // Several MB
openssl_public_encrypt($data, $encrypted, $publicKey);
// RSA max data size: (key_size/8) - 42 bytes for PKCS#1 v1.5 padding
// Encrypting 1MB with RSA-2048 fails — data too large// Hybrid encryption — correct approach:
// 1. Generate a random AES key
$sessionKey = random_bytes(32);
// 2. Encrypt the data with AES (fast)
$encryptedData = aesEncrypt($data, $sessionKey);
// 3. Encrypt the AES key with RSA (small — just 32 bytes)
openssl_public_encrypt($sessionKey, $encryptedKey, $publicKey);
// Store: $encryptedKey + $encryptedData
// Decrypt: RSA decrypt $encryptedKey → AES decrypt $encryptedData