Base32hex Encoder and Decoder

What is Base32hex?

Base32hex is the "Base 32 Encoding with Extended Hex Alphabet" defined in section 7 of RFC 4648. It works exactly like standard Base32: each character carries 5 bits, every 5 bytes become 8 characters, and the output is padded with = to a multiple of 8. Only the alphabet differs. Instead of A-Z 2-7, Base32hex continues counting where hexadecimal stops: the digits 0 to 9 stand for 0 to 9, A is 10 and V is 31.

Because the two alphabets share most of their characters, a Base32hex string can often be fed to a standard Base32 decoder without an error, but the bytes that come out are wrong. Always decode with the same variant that was used to encode.

Sort order is preserved

The alphabet is in ascending ASCII order and each character's value grows with its position. As a result, comparing two Base32hex strings character by character gives the same order as comparing the underlying bytes. RFC 4648 points this out as the property that standard Base32 and Base64 lack, and it makes Base32hex a good fit for keys in sorted storage such as databases and key-value stores.

Keep all strings in one letter case, and turn padding off when the inputs differ in length: the = sign sorts between the digits and the letters and can break the order.

Base32hex in DNSSEC NSEC3

NSEC3 records, defined in RFC 5155, prove that a DNS name does not exist while making it harder to list every name in the zone. Each name is hashed with SHA-1, and the 20-byte hash is written as a 32-character Base32hex label without padding, usually shown in lowercase. Because the encoding keeps the order of the hashes, the hashed names form a sorted chain. To turn a hash into such a label, paste it as hex input, turn padding off and choose Lowercase. This tool performs only the encoding step; it does not compute the salted, iterated NSEC3 hash.

Base32hex in code

# Python 3.10+
import base64
base64.b32hexencode(b'foobar')          # b'CPNMUOJ1E8======'
base64.b32hexdecode('CPNMUOJ1E8======') # b'foobar'

// Go (import "encoding/base32")
base32.HexEncoding.EncodeToString(data)
base32.HexEncoding.WithPadding(base32.NoPadding).EncodeToString(data)