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Encoding

Encoding transforms data from one representation to another without compression or encryption. Unlike encryption, encoding does not use keys and provides no security — it is purely a format transformation. This page covers the encoding schemes used in the sHEL project for safe data transport through restricted channels.

Overview

What this page covers

This page documents encoding schemes for data transformation:

  • Base64 (RFC 4648) — Binary-to-text encoding for data URIs and MIME
  • URL Encoding — Percent-encoding for safe URL transmission
  • HTML Entities — Character encoding for browser contexts
  • Hexadecimal — Byte-to-text representation
  • Format Comparison — Size, safety, and readability matrix

For Base64 in the context of the XML Project, see Base64 Encoding. For compression algorithms, see Compression. For encryption, see Encryption.

Base64 (RFC 4648)

Base64 encodes binary data using 64 printable ASCII characters. It is the standard mechanism for embedding binary data in text-based formats.

flowchart LR
    subgraph Input["Binary Input"]
        direction TB
        B1["01001000 01100101"]
        B2["01101100 01101100"]
        B3["01101111"]
    end

    subgraph Process["Base64 Process"]
        P1["Split into<br/>6-bit groups"]
        P2["Map to<br/>A-Z a-z 0-9 + /"]
        P3["Pad with =<br/>if needed"]
    end

    subgraph Output["Base64 Output"]
        O1["SGVs bG8="]
    end

    Input --> P1 --> P2 --> P3 --> Output

    style Input fill:#4a90d9
    style Output fill:#7ed321
Variant Alphabet Padding Use Case
Standard [A-Za-z0-9+/] = Email (MIME), data URIs
URL-safe [A-Za-z0-9-_] = or none URL parameters, filenames
Base64 for filenames [A-Za-z0-9+-] none Unix filenames

PowerShell

PowerShell
# Encode
$base64 = [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("text"))

# Decode
$text = [Text.Encoding]::UTF8.GetString([Convert]::FromBase64String($base64))

URL Encoding (Percent-Encoding)

URL encoding replaces unsafe ASCII characters with a % followed by two hexadecimal digits. Defined in RFC 3986.

Character Encoded Character Encoded
space %20 or + & %26
? %3F = %3D
/ %2F # %23
PowerShell
[System.Web.HttpUtility]::UrlEncode("hello world & test")
# Output: hello+world+%26+test

[System.Web.HttpUtility]::UrlDecode("hello+world+%26+test")
# Output: hello world & test

HTML Entities

HTML entity encoding prevents browser interpretation of special characters as markup.

Character Entity Numeric Must Encode In
& &amp; &#38; All contexts
< &lt; &#60; Element content, attributes
> &gt; &#62; Element content
" &quot; &#34; Double-quoted attributes
' &#x27; &#39; Single-quoted attributes

Hexadecimal Encoding

Hex encoding represents each byte as two hexadecimal characters (0-9, A-F). It doubles the size of the data but is human-readable and safe for all text contexts.

PowerShell
# Encode to hex
$hex = -join ([Text.Encoding]::UTF8.GetBytes("text") | ForEach-Object { $_.ToString("x2") })
# Output: 74657874

# Decode from hex
$bytes = for ($i = 0; $i -lt $hex.Length; $i += 2) {
    [Convert]::ToByte($hex.Substring($i, 2), 16)
}
[Text.Encoding]::UTF8.GetString($bytes)

Character Encoding Comparison

Encoding Output Size (relative to binary) Safe for URLs Safe for HTML Human Readable
Base64 133% Standard: No; URL-safe: Yes Yes Partially
Hex 200% Yes Yes Yes
URL Encode Variable (100-300%) Yes Partially Yes
HTML Entities Variable (100-500%) No Yes Yes