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1 | # keycask design |
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2 | |
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3 | Swift password manager: a shared core library, a command-line tool for |
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4 | macOS, Linux, and Windows, and later an iOS/macOS app and an AutoFill |
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5 | extension. This document covers the core and the CLI. The app and the |
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6 | extension get their own specs on top of a working core. |
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7 | |
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8 | The repository history before this commit was a Rust program of the same |
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9 | name. Nothing here is constrained by it: not the vault format, not the |
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10 | command set, not the tests. |
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11 | |
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12 | ## Goals |
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13 | |
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14 | - One vault file, encrypted with a passphrase, readable by every target |
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15 | including a sandboxed iOS app. |
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16 | - A core library with no platform dependencies beyond Foundation and |
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17 | swift-crypto, so the CLI and the apps share all logic. |
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18 | - A CLI that covers daily use and is scriptable: `--json` on reads, |
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19 | stable exit codes, a non-interactive passphrase path. |
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20 | - Identical behavior on macOS, Linux, and Windows, verified by one test |
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21 | suite. |
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22 | |
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23 | ## Non-goals for this slice |
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24 | |
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25 | - The app and the AutoFill extension. |
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26 | - Sync of any kind. |
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27 | - TOTP, import/export, audit, password history, multiple recipients, |
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28 | changing the passphrase, QR output, man pages, shell completions. |
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29 | - Reading vaults from the Rust version. |
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30 | - A config file. |
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31 | |
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32 | ## Repository and package |
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33 | |
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34 | One SwiftPM package at the repository root. `swift-tools-version:6.4`, |
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35 | Swift 6 language mode. |
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36 | |
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37 | ``` |
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38 | Package.swift |
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39 | Sources/KeycaskCore/ library: model, envelope, generator, resolution, wordlist |
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40 | Sources/keycask/ executable: ArgumentParser commands, paths, prompt, clipboard, atomic write |
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41 | Tests/KeycaskCoreTests/ Swift Testing, in-process |
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42 | Tests/KeycaskCLITests/ Swift Testing, spawns the built binary |
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43 | docs/superpowers/specs/ |
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44 | .gitbay/ci.yml |
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45 | LICENSE (0BSD), NOTICE, README.md, .gitignore |
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46 | ``` |
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47 | |
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48 | Dependencies: `apple/swift-crypto` and `apple/swift-argument-parser`. |
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49 | Nothing else. `Package.resolved` is committed. |
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50 | |
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51 | `KeycaskCore` imports Foundation and Crypto only. It never imports |
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52 | ArgumentParser, AppKit, UIKit, or spawns a process. Everything that |
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53 | touches a terminal, a path convention, the clipboard, or a subprocess |
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54 | lives in the executable target. A future app target links `KeycaskCore` |
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55 | and supplies its own versions of those pieces. |
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56 | |
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57 | `platforms:` in the manifest lists `.macOS(.v14)` and `.iOS(.v17)`. That |
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58 | sets Apple minimums only and has no effect on Linux or Windows. |
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59 | |
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60 | ## Vault file format |
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61 | |
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62 | The file is a JSON envelope. It is inspectable with any JSON tool and |
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63 | versioned without a hand-written binary parser. |
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64 | |
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65 | ```json |
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66 | { |
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67 | "format": 1, |
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68 | "kdf": { |
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69 | "name": "pbkdf2-hmac-sha256", |
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70 | "iterations": 600000, |
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71 | "salt": "<base64, 16 random bytes>" |
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72 | }, |
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73 | "box": "<base64, ChaCha20-Poly1305 combined nonce || ciphertext || tag>" |
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74 | } |
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75 | ``` |
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76 | |
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77 | - Key: 32 bytes from PBKDF2-HMAC-SHA256 over the passphrase, encoded as |
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78 | UTF-8 after NFC normalization, with the salt and iteration count from |
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79 | the envelope. PBKDF2 comes from swift-crypto's `_CryptoExtras`. |
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80 | - Salt: 16 random bytes generated by `init`, kept unchanged across saves. |
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81 | - Nonce: 12 random bytes, fresh on every save. `box` is the |
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82 | `ChaChaPoly.SealedBox.combined` bytes. |
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83 | - Plaintext: the JSON-encoded vault from the next section. |
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84 | - No additional authenticated data. |
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85 | |
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86 | Decryption outcomes: |
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87 | |
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88 | - Authentication failure, for any reason including a wrong passphrase, |
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89 | is "cannot decrypt". The two cases are never distinguished. |
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90 | - A file that is not valid JSON, does not match the envelope shape, has |
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91 | an unknown `kdf.name`, or has a `format` other than 1 is "corrupt". |
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92 | - Plaintext that decrypts but does not decode as a vault is "corrupt". |
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93 | |
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94 | Writing an envelope reuses the salt and iteration count of the envelope |
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95 | that was read, so a vault created with one KDF setting keeps it until a |
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96 | future explicit rekey command exists. |
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97 | |
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98 | ## Data model |
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99 | |
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100 | ```swift |
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101 | public struct Vault: Codable, Sendable { |
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102 | public var entries: [Entry] |
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103 | } |
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104 | |
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105 | public struct Entry: Codable, Sendable { |
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106 | public let id: EntryID |
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107 | public var name: String |
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108 | public var username: String? |
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109 | public var password: String |
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110 | public var url: String? |
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111 | public var notes: String? |
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112 | public var tags: [String] |
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113 | public let created: Date |
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114 | public var updated: Date |
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115 | } |
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116 | ``` |
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117 | |
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118 | - `EntryID` is eight characters from the alphabet `a-z` without `l` and |
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119 | `o`, plus digits `2-9`: 32 symbols, 40 bits. IDs are generated with |
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120 | `SystemRandomNumberGenerator` and checked for uniqueness against the |
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121 | vault on insert. They are shown in every listing. Names are labels and |
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122 | may repeat; the ID is the identity. |
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123 | - `tags` is kept sorted and free of duplicates, with case preserved, by |
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124 | the mutation methods on `Vault`. Comparison for `--tag` filters is |
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125 | case-insensitive. |
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126 | - Dates are ISO 8601 in UTC with whole-second precision. |
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127 | - Encoding uses sorted keys and a fixed date strategy so the same vault |
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128 | always produces the same plaintext bytes. Foundation's `UUID` is not |
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129 | used anywhere. |
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130 | |
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131 | `Vault` exposes: `add(_:)`, `remove(id:)`, `update(id:_:)`, |
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132 | `resolve(_ ref: String) throws -> Entry`, `filter(tag:)`, |
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133 | `search(_ query: String)`. |
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134 | |
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135 | ## Resolution |
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136 | |
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137 | Every command that names an entry takes a `REF`. |
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138 | |
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139 | 1. If `REF` equals an entry's ID, that entry. |
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140 | 2. Otherwise, if exactly one entry has `name == REF`, that entry. |
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141 | 3. Otherwise, if several entries have that name, error "ambiguous", |
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142 | listing each candidate's ID, username, and URL. Exit 5. |
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143 | 4. Otherwise, error "not found". Exit 3. |
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144 | |
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145 | There is no prefix matching. IDs are short by design so they are typed |
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146 | whole. A name that happens to equal another entry's ID resolves to the |
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147 | ID; the listing shows both, so the user can see it. |
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148 | |
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149 | ## CLI |
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150 | |
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151 | Built with swift-argument-parser. Root command `keycask`, global option |
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152 | `--vault PATH`. |
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153 | |
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154 | | Command | Behavior | |
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155 | |---|---| |
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156 | | `init` | Prompts for the passphrase twice, creates an empty vault. Fails with exit 1 if the file exists. | |
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157 | | `add NAME [-u USER] [--url URL] [--notes TEXT] [--tag T]... [--generate] [--length N] [--words N]` | Prompts for the password unless `--generate` or `--words` is given. Prints the new ID. | |
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158 | | `show REF [--reveal] [--field NAME] [--json]` | Text: one field per line, password masked unless `--reveal`. `--field` prints that one value raw, with no masking, for scripts. | |
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159 | | `ls [--tag T] [--json]` | One row per entry: id, name, username, url. Sorted by name, then id. | |
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160 | | `find QUERY [--json]` | Case-insensitive substring match over name, username, url, notes, and tags. Same output shape as `ls`. | |
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161 | | `edit REF [--name N] [-u USER] [--url URL] [--notes TEXT] [--tag T]... [--untag T]... [--password] [--generate] [--length N] [--words N]` | Applies the given changes. `--password` prompts. Any change sets `updated`. No flags is a usage error. | |
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162 | | `rm REF [--yes]` | Asks for confirmation on a TTY unless `--yes`. Without a TTY and without `--yes`, exit 2. | |
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163 | | `generate [--length N] [--words N] [--copy]` | Prints a password. Does not open the vault. `--copy` goes to the clipboard instead of stdout. | |
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164 | | `clip REF [--field NAME]` | Copies the field (default `password`) and clears it after 45 seconds if the clipboard still holds it. | |
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165 | | `clipboard-daemon` | Hidden. The detached child that performs the delayed clear. | |
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166 | |
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167 | Output rules: |
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168 | |
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169 | - `--json` emits one object (`show`) or an array (`ls`, `find`) of |
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170 | entries with the same field names as the model. `password` is the |
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171 | string `"********"` unless `--reveal`. |
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172 | - Text output goes to stdout. Errors go to stderr as one line. |
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173 | - `--length` defaults to 24. The character alphabet is ASCII upper, |
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174 | lower, digits, and the symbols `!@#$%^&*()-_=+[]{};:,.<>?`. Every |
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175 | character is drawn uniformly with `SystemRandomNumberGenerator`. |
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176 | - `--words N` takes an explicit count. `generate` with neither `--length` |
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177 | nor `--words` produces a 24-character password. Words come from the EFF long list, |
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178 | joined with `-`. The list is embedded as one multi-line string literal |
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179 | in `KeycaskCore` and split on first use. Attribution goes in `NOTICE`. |
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180 | - `--generate` and `--words` together is a usage error. |
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181 | |
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182 | Passphrase input: if `KEYCASK_PASSPHRASE` is set, its value is used. It |
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183 | exists so tests and scripts run unattended. Otherwise the CLI prompts on |
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184 | the terminal with echo off. No TTY and no variable is exit 2. |
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185 | |
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186 | Exit codes: |
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187 | |
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188 | | Code | Meaning | |
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189 | |---|---| |
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190 | | 0 | ok | |
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191 | | 1 | failure (I/O, vault exists, clipboard tool missing, and anything else) | |
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192 | | 2 | usage, including ArgumentParser validation errors and missing passphrase | |
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193 | | 3 | not found (entry, or vault file) | |
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194 | | 4 | cannot decrypt | |
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195 | | 5 | ambiguous name | |
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196 | |
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197 | ArgumentParser exits with 64 on validation errors by default. `main` |
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198 | calls `parseAsRoot()` inside `do/catch`, prints |
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199 | `fullMessage(for:)` to stderr, and exits 2 instead. |
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200 | |
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201 | ## Platform layer |
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202 | |
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203 | All in the executable target, each behind a small function with a Unix |
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204 | and a Windows body where they differ. |
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205 | |
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206 | - **Vault path.** `--vault`, else `$KEYCASK_VAULT`, else |
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207 | `$XDG_DATA_HOME/keycask/vault.kc`, else |
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208 | `$HOME/.local/share/keycask/vault.kc`. On Windows: |
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209 | `%LOCALAPPDATA%\keycask\vault.kc`. The directory is created on write. |
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210 | - **Atomic write.** Write to `<name>.tmp` beside the target, fsync, |
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211 | rename over the target. Unix opens the temp file with mode 0600. |
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212 | Windows uses `MoveFileExW` with `MOVEFILE_REPLACE_EXISTING` because |
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213 | `rename` fails on an existing target there. The temp file is removed |
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214 | on any failure. |
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215 | - **Prompt.** Reads a line from the terminal with echo off: termios on |
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216 | Unix, `SetConsoleMode` without `ENABLE_ECHO_INPUT` on Windows. |
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217 | Restores the mode afterwards, including on error. |
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218 | - **Clipboard.** Shell out to the first tool found: `pbcopy`/`pbpaste` |
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219 | on macOS; `wl-copy`/`wl-paste`, then `xclip -selection clipboard`, on |
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220 | Linux; `clip.exe` to write and `powershell -command Get-Clipboard` to |
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221 | read on Windows. No tool found is exit 1 with a message naming the |
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222 | tools. `clip` spawns `keycask clipboard-daemon` detached with stdout |
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223 | and stderr to null, writes `{"secret": ..., "previous": ...}` to its |
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224 | stdin, and exits without waiting. The daemon sets the clipboard, |
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225 | sleeps 45 seconds, reads the clipboard, and if it still equals the |
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226 | secret restores `previous` or clears when `previous` is empty. |
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227 | |
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228 | ## Errors |
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229 | |
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230 | One `KeycaskError` enum in `KeycaskCore` with a case per situation and an |
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231 | `exitCode` and `message` property. Foundation and Crypto errors are |
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232 | wrapped into it at the call site that produced them; nothing outside |
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233 | `KeycaskCore` sees a raw `CryptoKitError` or `CocoaError`. The |
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234 | executable's `main` catches `KeycaskError`, prints `message` to stderr, |
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235 | and exits with `exitCode`. Any other error is a bug and exits 1 with its |
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236 | description. |
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237 | |
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238 | ## Testing |
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239 | |
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240 | Swift Testing on all targets. |
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241 | |
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242 | Core, in process: |
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243 | |
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244 | - Envelope: encrypt then decrypt round-trips; wrong passphrase is |
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245 | `cannotDecrypt`; one flipped byte in `box` is `cannotDecrypt`; |
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246 | non-JSON, wrong `format`, and unknown `kdf.name` are `corrupt`; the |
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247 | salt is preserved across a save and the nonce is not; a PBKDF2 vector |
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248 | from a published source matches. |
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249 | - Model: encoding the same vault twice yields identical bytes; tags are |
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250 | sorted and unique after every mutation; `updated` changes on update. |
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251 | - ID: length 8, alphabet as specified, insert rejects a duplicate. |
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252 | - Resolution: ID beats name; unique name resolves; repeated name is |
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253 | `ambiguous` with all candidates; unknown is `notFound`. |
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254 | - Generator: requested length; only alphabet characters; word count and |
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255 | separator; every word is in the list. |
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256 | - Search: case-insensitive, matches each searchable field, no match |
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257 | returns empty. |
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258 | |
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259 | CLI, black box: |
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260 | |
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261 | - Locates the built `keycask` binary from the test bundle's products |
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262 | directory. |
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263 | - Each test gets its own temp directory and runs the binary with |
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264 | `KEYCASK_VAULT` pointing into it and `KEYCASK_PASSPHRASE` set. Tests |
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265 | are independent and may run in parallel. |
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266 | - Covers every command's happy path, every exit code, `--json` shape, |
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267 | masking versus `--reveal`, `--field` raw output, the ambiguous-name |
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268 | listing, `rm` without `--yes` and without a TTY, `edit` with no flags, |
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269 | `--generate` with `--words`, and `init` on an existing vault. |
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270 | - The clipboard daemon's restore decision is unit-tested in process; |
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271 | the tests do not touch the real clipboard. |
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272 | |
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273 | The CLI suite is the conformance suite. When the app exists, its |
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274 | behavior is checked against the same expectations. |
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275 | |
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276 | ## CI and release |
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277 | |
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278 | `.gitbay/ci.yml`, Linux runner: |
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279 | |
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280 | 1. Install swiftly into `$HOME` if missing, then the Swift 6.4 |
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281 | toolchain. `$HOME` persists across builds so this is a one-time cost. |
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282 | 2. `swift format lint --strict --recursive Sources Tests` |
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283 | 3. `swift build` |
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284 | 4. `swift test` |
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285 | |
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286 | macOS and Windows are built and tested by hand until runners exist for |
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287 | them. |
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288 | |
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289 | Releases are annotated git tags `vX.Y.Z`. The Homebrew formula lives in |
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290 | a separate tap repository and builds the tagged source with |
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291 | `swift build -c release --product keycask`. Prebuilt Linux and Windows |
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292 | binaries are a later addition. |
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293 | |
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294 | ## Workflow |
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295 | |
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296 | The root commit of this history is the wipe: this spec, the license, |
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297 | `.gitignore`, and a README skeleton, pushed directly to `main`. Every |
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298 | change after it goes through a branch and a merge request. |