Why use Base45 instead of Base64 in a QR code?

Base64 forces a QR code into byte mode, which stores 8 bits per character. Base45 uses only characters available in QR alphanumeric mode, which packs 5.5 bits per character — the resulting QR symbol is meaningfully smaller and scans faster.

What does the HC1: prefix mean?

HC1 is the Health Certificate version 1 context identifier used by the EU Digital COVID Certificate. Everything after the colon is the Base45 payload.

My decoded output looks like binary garbage — is that wrong?

Probably not. Base45 payloads are usually zlib-compressed CBOR, so the raw bytes are not text. Inflate them first, then parse the CBOR/COSE structure.

Base45 Decoder

Decode Base45 payloads used in EU Digital COVID Certificates and QR code data.

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RAW INPUT

DECODED

Output appears here as you type — decoded on your device.

Input is processed on your device. Nothing you paste is sent anywhere.

What is the Base45 Decoder?

Base45 is a binary-to-text encoding that maps every 2 bytes onto 3 characters from a 45-symbol alphabet chosen to fit the QR code alphanumeric mode, making QR codes that carry it significantly smaller.

Base45 exists for one reason: QR codes. QR's alphanumeric mode can store 45 specific characters (0–9, A–Z, space and eight punctuation marks) far more densely than its byte mode. Base45 encodes binary data using exactly that alphabet, so a certificate that would need a large byte-mode QR fits into a much smaller, faster-scanning symbol.

It is specified in IETF draft-faltstrom-base45 and became widely deployed through the EU Digital COVID Certificate, where the payload chain runs CBOR → COSE signature → zlib → Base45 → QR, prefixed with 'HC1:'. Decoding Base45 is the first step in unwrapping any of those payloads.

Paste the Base45 string — with or without the HC1: prefix — and the decoder returns the underlying bytes, which are typically a zlib-compressed COSE structure you can then inflate.

Base45 Decoder at a glance

Specification: draft-faltstrom-base45 (IETF)
Alphabet: 45 chars: 0–9 A–Z space $%*+-./:
Ratio: 3 characters per 2 bytes (+50%)
Best known use: EU Digital COVID Certificate (HC1:)

How to use the Base45 Decoder

1Paste the Base45 string; strip or keep the HC1: prefix — both are handled.
2Read the decoded bytes in the output panel.
3If the result looks like compressed data, pass it to the Gzip/Zlib Decompressor to inflate it.

When you would reach for it

Unwrapping the payload of an EU Digital COVID Certificate QR code.
Debugging a QR code that uses alphanumeric mode to keep the symbol small.
Working through a CTF or forensics challenge that layers Base45 over compression.

Base45 Decoder — frequently asked questions

Last reviewed 25 July 2026 · questions or corrections: contact@decoder.tools