A cryptographic nonce is an arbitrary, single-use random number generated for cryptographic communications to prevent replay attacks and secure CSP scripts.
A Nonce (Number used ONCE) is a pseudorandom or pseudo-unique token generated for a single cryptographic operation, authentication handshake, or HTTP transaction. In web security, nonces prevent replay attacks (in OAuth/OIDC), ensure uniqueness in symmetric encryption (AES-GCM Initialization Vectors), and whitelist dynamic inline scripts in Content Security Policies (script-src 'nonce-...').
Construct Content Security Policies with the CSP Builder or generate cryptographically secure random tokens using the Password & Token Generator.
A per-request cryptographic nonce generated on the server is attached to valid <script nonce="rAnd0m..."> tags and matched against the Content-Security-Policy: script-src 'nonce-rAnd0m...' header to prevent Cross-Site Scripting (XSS).
Clients pass a random nonce in authentication requests. The identity provider embeds the identical nonce inside the signed ID token, guaranteeing the token was not intercepted and replayed.
Free, browser-based utilities to test, generate, and inspect Cryptographic Nonce (Number Used Once) payloads directly.
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