Data & cryptography
Technical guides about data & cryptography, written for practical follow-up.
Latest guides
16 articlesJWT validation: signatures, claims and the key you actually trust
Work through a token-verification decision using issuer, audience, expiry and an independently trusted key.
Verify a download checksum without confusing integrity with trust
Compare complete digests, obtain the expected value independently and understand when a signature gives stronger evidence.
Browser file encryption: plan the password and recovery test first
Understand authenticated encryption, the vault format and a safe round-trip workflow before deleting or moving source files.
Why identical-looking text produces different hashes
Inspect UTF-8 bytes, Unicode normalisation and line endings before comparing text digests across applications.
Verify webhook HMACs using the original request bytes
Define the signed message, key encoding, timestamp window and replay rules before comparing a webhook signature.
Password breach checks: what a range query can tell you
Understand hash prefixes, padded responses and corpus limits, then choose a practical response to a match.
UUIDv4 identifiers: randomness, collisions and validation
Read the version and variant bits, estimate collision risk responsibly and keep identifiers separate from access control.
Generate passwords around a password-manager workflow
Choose length and character rules with an explicit threat model, then handle storage, recovery and service restrictions.
Design random tokens with enough entropy and a clear expiry
Convert a byte budget into encoded length, store verifiers safely and plan single-use and revocation behaviour.
Review a HAR archive before it reaches a support ticket
Inspect request and response data, remove application-specific secrets and verify that redaction preserves a useful reproduction.
Base64 and Base64url: decode bytes without losing Unicode
Work through padding, alphabet differences and UTF-8 conversion, including why encoding is not encryption.
Hexadecimal data: bytes, text and endianness
Read hex pairs, recognise malformed input and decide when a byte sequence should be decoded as text or a number.
JSON validation beyond a missing comma
Separate syntax, duplicate member names, numeric precision and schema requirements when reviewing an API payload.
Unix timestamps: seconds, milliseconds and timezone mistakes
Recognise units, preserve range and reproduce daylight-saving errors without treating a timestamp as a local clock reading.
That HAR file might be your login.
Before attaching a network trace to a support ticket, check the credentials and application data that may be travelling with it.
Hashing and encryption do different jobs.
A file checksum, an encrypted vault and a breach lookup can all involve cryptography. Knowing which question each answers prevents expensive mistakes.
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16 guides