Data encoding

Covers the 102 data bits (2 TNID variant + 100 payload), written as the 17 characters after the . in a TNID string: 17 characters × 6 bits.

Why 17 characters

The name has its own encoding and the 6 UUID version and variant bits are constants, leaving 102 bits. 102 = 17 × 6: no padding.

Alphabet

64 values, in ASCII order, so encoded strings sort like their bits:

-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz

Value = position in this string, from 0. Full table under Mapping.

Not base64

Same 64 characters as base64url (RFC 4648), different order, so different output for the same bits. Don't use a base64 library.

String layout

One symbol per bit, one group per hex digit. 1–9, A–H are the 17 encoded characters in order; 6-bit characters straddle 4-bit nibbles:

nnnn.nnnn.nnnn.nnnn.nnnn.1111.1122.2222-
3333.3344.4444.5555-
vvvv.5566.6666.7777-
uutt.8888.8899.9999-
AAAA.AABB.BBBB.CCCC.CCDD.DDDD.EEEE.EEFF.FFFF.GGGG.GGHH.HHHH

Symbol	Bits	Role
`n`	20	Name, not part of the data
`v`	4	UUID version, skipped
`u`	2	UUID variant, skipped
`t`	2	TNID variant: last 2 bits of character 7
`1`–`9`, `A`–`H`	6 each	The 17 encoded characters

Characters	Bits
1–6	First 40 payload bits
7	4 payload bits, then 2 TNID variant bits
8–17	Last 60 payload bits

Worked example

Data part of user.Br2flcNDfF6LYICnT = d6157337-0ebc-8686-83ab-4075a34cdcde. Character 7, N = 011000, ends in 00: variant 0.

#	Char	Bits	Value
1	`B`	`001100`	12
2	`r`	`110111`	55
3	`2`	`000011`	3
4	`f`	`101011`	43
5	`l`	`110001`	49
6	`c`	`101000`	40
7	`N`	`011000`	24
8	`D`	`001110`	14
9	`f`	`101011`	43
10	`F`	`010000`	16
11	`6`	`000111`	7
12	`L`	`010110`	22
13	`Y`	`100011`	35
14	`I`	`010011`	19
15	`C`	`001101`	13
16	`n`	`110011`	51
17	`T`	`011110`	30

Mapping

Read each column top to bottom.

000000 -   010000 F   100000 V   110000 k
000001 0   010001 G   100001 W   110001 l
000010 1   010010 H   100010 X   110010 m
000011 2   010011 I   100011 Y   110011 n
000100 3   010100 J   100100 Z   110100 o
000101 4   010101 K   100101 _   110101 p
000110 5   010110 L   100110 a   110110 q
000111 6   010111 M   100111 b   110111 r
001000 7   011000 N   101000 c   111000 s
001001 8   011001 O   101001 d   111001 t
001010 9   011010 P   101010 e   111010 u
001011 A   011011 Q   101011 f   111011 v
001100 B   011100 R   101100 g   111100 w
001101 C   011101 S   101101 h   111101 x
001110 D   011110 T   101110 i   111110 y
001111 E   011111 U   101111 j   111111 z