89 lines
3.2 KiB
Markdown
89 lines
3.2 KiB
Markdown
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---
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obj: concept
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wiki: https://en.wikipedia.org/wiki/Base64
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rfc: https://datatracker.ietf.org/doc/html/rfc4648
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---
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# Base64
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Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an [ASCII](ASCII.md) string format by translating it into a radix-64 representation.
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When the term "Base64" is used on its own to refer to a specific algorithm, it typically refers to the version of Base64 outlined in RFC 4648, section 4, which uses the following alphabet to represent the radix-64 digits, alongside = as a padding character:
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```
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ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
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```
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A common variant is "Base64 URL safe", which omits the padding and replaces `+/` with `-_` to avoid characters that might cause problems in [URL](../internet/URL.md) path segments or query parameters.
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Base64 encoding schemes are commonly used to encode binary data for storage or transfer over media that can only deal with [ASCII](ASCII.md) text (or some superset of [ASCII](ASCII.md) that still falls short of accepting arbitrary binary data). This ensures that the data remains intact without modification during transport. Common applications of Base64 include:
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- [Email](../internet/eMail.md) via [MIME](MIME.md)
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- Storing complex data in [XML](XML.md)
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- Encoding binary data so it can be included in a [Data URL](../internet/Data%20URLs.md)
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## Alphabet
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| Index | Binary | Char |
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| ------- | ------ | ---- |
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| 0 | 000000 | `A` |
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| 1 | 000001 | `B` |
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| 2 | 000010 | `C` |
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| 3 | 000011 | `D` |
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| 4 | 000100 | `E` |
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| 5 | 000101 | `F` |
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| 6 | 000110 | `G` |
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| 7 | 000111 | `H` |
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| 8 | 001000 | `I` |
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| 9 | 001001 | `J` |
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| 10 | 001010 | `K` |
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| 11 | 001011 | `L` |
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| 12 | 001100 | `M` |
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| 13 | 001101 | `N` |
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| 14 | 001110 | `O` |
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| 15 | 001111 | `P` |
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| 16 | 010000 | `Q` |
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| 17 | 010001 | `R` |
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| 18 | 010010 | `S` |
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| 19 | 010011 | `T` |
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| 20 | 010100 | `U` |
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| 21 | 010101 | `V` |
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| 22 | 010110 | `W` |
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| 23 | 010111 | `X` |
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| 24 | 011000 | `Y` |
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| 25 | 011001 | `Z` |
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| 26 | 011010 | `a` |
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| 27 | 011011 | `b` |
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| 28 | 011100 | `c` |
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| 29 | 011101 | `d` |
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| 30 | 011110 | `e` |
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| 31 | 011111 | `f` |
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| 32 | 100000 | `g` |
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| 33 | 100001 | `h` |
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| 34 | 100010 | `i` |
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| 35 | 100011 | `j` |
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| 36 | 100100 | `k` |
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| 37 | 100101 | `l` |
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| 38 | 100110 | `m` |
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| 39 | 100111 | `n` |
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| 40 | 101000 | `o` |
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| 41 | 101001 | `p` |
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| 42 | 101010 | `q` |
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| 43 | 101011 | `r` |
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| 44 | 101100 | `s` |
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| 45 | 101101 | `t` |
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| 46 | 101110 | `u` |
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| 47 | 101111 | `v` |
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| 48 | 110000 | `w` |
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| 49 | 110001 | `x` |
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| 50 | 110010 | `y` |
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| 51 | 110011 | `z` |
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| 52 | 110100 | `0` |
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| 53 | 110101 | `1` |
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| 54 | 110110 | `2` |
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| 55 | 110111 | `3` |
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| 56 | 111000 | `4` |
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| 57 | 111001 | `5` |
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| 58 | 111010 | `6` |
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| 59 | 111011 | `7` |
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| 60 | 111100 | `8` |
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| 61 | 111101 | `9` |
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| 62 | 111110 | `+` |
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| 63 | 111111 | `/` |
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| Padding | - | = |
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