base 45 encode
Internet-Draft Base45 April 2021
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Interpretation of Encoded Data . . . . . . . . . . . . . . . 2
4. The Base 45 Encoding . . . . . . . . . . . . . . . . . . . . 2
4.1. When to use Base45 . . . . . . . . . . . . . . . . . . . 3
4.2. The alphabet used in Base45 . . . . . . . . . . . . . . . 3
4.3. Encoding example . . . . . . . . . . . . . . . . . . . . 3
4.4. Decoding example . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
When using QR or Aztec codes a different encoding scheme is needed
than the already established base 64, base 32 and base 16 encoding
schemes that are described in RFC 4648 [RFC4648]. The difference
from those and base 45 is the key table and that the padding with '='
is not required.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Interpretation of Encoded Data
Encoded data is to be interpreted as described in RFC 4648 [RFC4648]
with the exception that a different alphabet is selected.
4. The Base 45 Encoding
A 45-character subset of US-ASCII is used, the 45 characters that can
be used in a QR or Aztec code. If we look at Base 64, it encodes 3
bytes in 4 characters. Base 45 encodes 2 bytes in 3 characters.
The two bytes [A, B] are turned into [C, D, E] where (A*256) + B = C
+ (D*45) + (E*45*45). The values C, D and E are then looked up in
Table 1 to produce a three character string and the reverse when
decoding.
Faltstrom, et al. Expires October 5, 2021 [Page 2]