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WebCrypto Keypair & HMAC Studio
Generate cryptographically authenticated RSA, ECDSA, and HMAC keys directly in browser memory using W3C SubtleCrypto. Zero network transmissions, zero external dependencies.
Cryptographic Primality & Elliptic Curve Formulations
WebCrypto leverages hardware CSPRNG entropy and native C++ engine routines to guarantee mathematical security bounds:
1. RSA Factorization Modulus & Bit Entropy:
N = p × q, φ(N) = (p - 1)(q - 1), e · d ≡ 1 (mod φ(N))
Entropy H = log2(N) ≥ 2048 bits → Security level ≈ 112 bits (NIST SP 800-57)
2. ECDSA Point Multiplication over Weierstrass Curves:
y2 ≡ x3 - 3x + b (mod p) → Public Key Q = d · G
3. HMAC Key Transformation PRF:
HMAC(K, m) = H((K' ⊕ opad) || H((K' ⊕ ipad) || m))
5 Fatal Traps in Web Cryptography & Key Management
1. Storing Unencrypted Private Keys in localStorage
localStorage and sessionStorage are completely unencrypted and accessible synchronously to any JavaScript executing in the document origin. A single minor XSS vulnerability, rogue third-party CDN script, or compromised NPM bundle can instantly read and exfiltrate all stored private keys. Always wrap private keys with AES-GCM or store non-extractable keys in IndexedDB.
2. Non-Extractable Keys Wiped on Session Refresh
Setting
extractable: false when invoking crypto.subtle.generateKey() provides excellent defense-in-depth against memory scraping. However, if the CryptoKey object is not explicitly persisted to IndexedDB using structured cloning, a simple page refresh will irrevocably destroy the keypair forever.
3. ECDSA Ephemeral Nonce Reuse Catastrophe
ECDSA signing requires a cryptographically random, uniform ephemeral integer k for every single signature. Reusing the exact same nonce k across two distinct messages enables an observer to recover the private key d through elementary modular division:
d = (s1·m2 - s2·m1) / (r·(s2 - s1)) mod n. WebCrypto prevents this by generating nonces internally via CSPRNG.
4. Cross-Protocol Key Confusion (RSA-OAEP vs RSA-PSS)
Reusing the same underlying RSA modulus and private exponent for both decryption (RSA-OAEP) and digital signatures (RSA-PSS) creates catastrophic cross-protocol chosen-ciphertext vulnerabilities. WebCrypto strictly enforces key usage separation (
decrypt vs sign) at the engine level.
5. Deprecated RSA Key Lengths Below 2048 Bits
Generating 1024-bit RSA keys provides less than 80 bits of symmetric equivalence, making them vulnerable to distributed cloud factorizations using Number Field Sieve (NFS) algorithms. Modern security standards mandate a minimum of 2048 bits (112-bit security) or preferably 4096 bits / ECDSA P-256 (128-bit security).
Frequently Asked Technical Questions
Is it safe to generate cryptographic keys in a browser tool?+
Yes, because this tool relies strictly on the native W3C Web Cryptography API (window.crypto.subtle) running in isolated browser memory. Zero private keys, seeds, or signatures are ever transmitted over a network.
What is the difference between SPKI and PKCS#8?+
SubjectPublicKeyInfo (SPKI) is the standard format for encoding Public Keys in PEM format. PKCS#8 is the standard container for encoding Private Keys with optional encryption wrapping.
Why does WebCrypto forbid synchronous crypto operations?+
Asymmetric operations such as 4096-bit RSA key generation or modular exponentiation require billions of CPU cycles. Running them synchronously would freeze the browser UI thread. WebCrypto enforces asynchronous Promises to keep user interfaces fluid.
What is the difference between JWK (JSON Web Key) and PEM formatting?+
PEM (Privacy-Enhanced Mail) encodes binary DER ASN.1 structures in Base64 with header/footer armor. JWK (RFC 7517) represents cryptographic keys as native JSON objects with standardized properties (kty, crv, x, y, n, e).
When should I choose ECDSA over RSA?+
ECDSA (e.g. P-256) provides 128-bit security with only 256-bit keys, resulting in vastly smaller payload sizes, faster key generation, and reduced network overhead compared to equivalent 3072-bit RSA keys.
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