Base62 Implementations that do and don't agree

[coolaj86]

It seems that the algorithms associated with "base_x", GMP, GnuPG, and Bitcoin Base58 all seem to agree:
(at least in simple tests of a few dozen bytes or less)

• https://github.com/cryptocoinjs/base-x
• Could you provide sample output? oconnor663/basex_gmp#1
• Could you provide sample output? seruco/base62#4
• Which base62 implementations is this compatible with? brianhempel/base_x#1
• https://en.wikipedia.org/wiki/Base62

Disagree

• This is NOT base62. Does not agree with GMP / GnuPG / Saltpack packages lytics/base62#6, Is it base62 or (non-standard) base64 encoding? lytics/base62#3
• Does not agree with Saltpack / GMP jxskiss/base62#2
• Does not agree with GMP / GnuPG / Saltpack Base62 abhishekjhaji/go-base62#1

Unknown

• https://github.blog/2021-04-05-behind-githubs-new-authentication-token-formats/
• https://gmplib.org/
• https://github.com/eknkc/basex
• https://codeberg.org/ac/base62
• https://github.com/marksalpeter/token
• Which base62 algorithm does this implement? tuupola/base62#29

[coolaj86]

Reference Base62 Strings

Raw   : Hello, 世界 (13 bytes)
Base64: SGVsbG8sIOS4lueVjA (18 chars)
Base62: 1wJfrzvdbuFbL65vcS (18 chars)

Raw   : Hello World (11 bytes)
Base64: SGVsbG8gV29ybGQ (15 chars)
Base62: 73XpUgyMwkGr29M (15 chars)

Raw   : [0] (1 bytes)
Base64: AA (2 chars)
Base62: 00 (2 chars)

Raw   : [0 0 0 0 0 0 0 0 0 0 0 0] (12 bytes)
Base64: AAAAAAAAAAAAAAAA (16 chars)
Base62: 00000000000000000 (17 chars)

Raw   : [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] (24 bytes)
Base64: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA (32 chars)
Base62: 000000000000000000000000000000000 (33 chars)

Raw   : [0 0 0 0 255 255 255 255] (8 bytes)
Base64: AAAAAP____8 (11 chars)
Base62: 000004gfFC3 (11 chars)

Raw   : [255 255 255 255 0 0 0 0] (8 bytes)
Base64: _____wAAAAA (11 chars)
Base62: LygHZwPV2MC (11 chars)

Test Code Reference

package main

import (
	"encoding/base64"
	"fmt"

	"github.com/keybase/saltpack/encoding/basex"
)

func main() {
	for _, src := range [][]byte{
		[]byte("Hello, 世界"),
		[]byte("Hello World"),
		{0},
		{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
		{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
			0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
		{0, 0, 0, 0, 255, 255, 255, 255},
		{255, 255, 255, 255, 0, 0, 0, 0},
	} {
		b62 := basex.Base62StdEncoding.EncodeToString(src)
		b64 := base64.RawURLEncoding.EncodeToString(src)

		if src[0] == 0x0 || src[1] == 255 {
			fmt.Printf("Raw   : %v (%d bytes)\n", src, len(src))
		} else {
			fmt.Printf("Raw   : %v (%d bytes)\n", string(src), len(src))
		}
		fmt.Printf("Base64: %s (%d chars)\n", b64, len(b64))
		fmt.Printf("Base62: %s (%d chars)\n", b62, len(b62))
		fmt.Println("")
	}
}