authors==Huima status==Experimental title==The Bubble Babble Binary Data Encoding number==Internet Draft date==April 2000 Network Working Group Antti Huima Internet Draft SSH Communications Security draft-huima-babble-01.txt April 2000 corrected 2011 The Bubble Babble Binary Data Encoding Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Abstract This document describes a new encoding method for binary data that is intended to be used in conjunction with fingerprints of security-critical data. 1. Introduction Hash values of certificates and public keys, known as fingerprints or thumbprints, are commonly used for verifying that a received security-critical datum has been received correctly. Fingerprints are binary data and typically encoded as series of hexadecimal digits. However, long strings hexadecimal digits are difficult for comprehend and cumbersome to translate reliably e.g. over phone. The Bubble Babble Encoding encodes arbitrary binary data into pseudowords that are more natural to humans and that can be pronounced relatively easily. The encoding consumes asymptotically the same amount of space as an encoding of the form HH HH HH HH ... where `H' is a hexadecimal digit, i.e. carries 16 bits in six characters. However, the Bubble Babble Encoding includes a checksumming method that can sometimes detect invalid encodings. The method does not increase the length of the encoded data. 2. Encoding Below, _|X|_ denotes the largest integer not greater than X. Let the data to be encoded be D[1] ... D[K] where K is the length of the data in bytes; every D[i] is an integer from 0 to 2^8 - 1. First define the checksum series C[1] ... C[_|K/2|_ + 1] where C[1] = 1 C[n] = (C[n - 1] * 5 + (D[n * 2 - 3] * 7 + D[n * 2 - 2])) mod 36 The data is then transformed into _|K/2|_ `tuples' T[1] ... T[_|K/2|_] and one `partial tuple' P so that T[i] = where a = (((D[i * 2 - 1] >> 6) & 3) + C[i]) mod 6 b = (D[i * 2 - 1] >> 2) & 15 c = (((D[i * 2 - 1]) & 3) + _|C[i] / 6|_) mod 6 d = (D[i * 2] >> 4) & 15; and e = (D[i * 2]) & 15. The partial tuple P is P = where if K is even then a = (C[K/2 + 1]) mod 6 b = 16 c = _|C[K/2 + 1] / 6|_ but if it is odd then a = (((D[K] >> 6) & 3) + C[_|K/2|_ + 1]) mod 6 b = (D[K] >> 2) & 15 c = (((D[K]) & 3) + _|C[_|K/2|_ + 1] / 6|_) mod 6 The `vowel table' V maps integers between 0 and 5 to vowels as 0 - a 1 - e 2 - i 3 - o 4 - u 5 - y and the `consonant table' C maps integers between 0 and 16 to consonants as 0 - b 1 - c 2 - d 3 - f 4 - g 5 - h 6 - k 7 - l 8 - m 9 - n 10 - p 11 - r 12 - s 13 - t 14 - v 15 - z 16 - x Note well that the vowel and consonant tables are indexed from 0, while the data and checksum series are indexed from 1. The encoding E(T) of a tuple T = is then the string V[a] C[b] V[c] C[d] `-' C[e] where there are five characters, and `-' is the literal hyphen. The encoding E(P) of a partial tuple P = is the three-character string V[a] C[b] V[c]. Finally, the encoding of the whole input data D is obtained as `x' E(T[1]) E(T[2]) ... E(T[_|K/2|_]) E(P) `x' where `x's are literal characters. 3. Decoding Decoding is obviously the process of encoding reversed. To check the checksums, when a tuple or partial tuple has been recovered from the encoded string, an implementation should check that ((a - C[i]) mod 6) < 4 and that ((c - C[i]) mod 6) < 4. Otherwise the encoded string is not a valid encoding of any data and should be rejected. 4. Checksum Strength Every vowel in an encoded string carries 0.58 bits redundancy; thus the length of the `checksum' in the encoding of an input string containing K bytes is 0.58 * K bits. 5. Test Vectors ASCII Input Encoding ------------------------------------------------------------------ `' (empty string) `xexax' `1234567890' `xesef-disof-gytuf-katof-movif-baxux' `Pineapple' `xigak-nyryk-humil-bosek-sonax' 6. Author's Address Antti Huima SSH Communications Security, Ltd. [XXX] 7. Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. 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