Initial commit: CLI extraction from yubisignerHEADmain

Extract core signing logic from Stefan Claas's yubisigner GUI
into standalone CLI tool for automation workflows.

Features:
- YubiKey PIV Ed25519 signing (slot 9c)
- 4 hash algorithms (RIPEMD-256, SHA-256, SM3, Streebog-256)
- Identical signature format to original yubisigner
- Command-line interface for scripting

All cryptographic functions are verbatim copies from yubisigner.go
with original line number references preserved in comments.

1 files changed, 119 insertions, 0 deletions

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+# yubisigner-cli
+
+Command-line version of [yubisigner](https://github.com/Ch1ffr3punk/yubisigner) by Stefan Claas, for signing files with YubiKey PIV Ed25519 keys.
+
+## What is this?
+
+This is a CLI tool extracted from the original yubisigner GUI application. It provides the same cryptographic signing functionality but in a command-line interface suitable for scripting and automation.
+
+## Why CLI?
+
+The original yubisigner is a Fyne GUI application. To integrate YubiKey PIV signing with automated workflows like NeoMutt mail2news posting, a CLI version was needed.
+
+## How it was created
+
+This tool was created by extracting the core signing logic from the original `yubisigner.go`:
+
+### Extracted functions (with original line references)
+
+| Function | Original lines | Purpose |
+|----------|---------------|---------|
+| `normalizeToCRLF` | 538-544 | RFC-compliant line ending normalization |
+| `ensureUTF8` | 547-552 | UTF-8 validation and sanitization |
+| `calculateHashesRAM` | 1621-1640 | Calculate 4 hashes (RIPEMD-256, SHA-256, SM3, Streebog-256) |
+| `formatHashes` | 1746-1766 | Format hashes with right-aligned names |
+| `formatSignatureRFC` | 1996-2007 | Format signature with 64-char line breaks |
+| `openYubiKey` | 2073-2092 | Open YubiKey at specified index |
+| `signEd25519Data` | 1843-1862 | Sign data with Ed25519 (PIV slot 9c) |
+| `signDataInternal` | 1769-1840 | Main signing workflow (Ed25519 only) |
+
+### Constants preserved
+
+- `Ed25519SignatureSize`, `Ed25519PublicKeySize`, `Ed25519CombinedSize` (lines 95-99)
+- `AlgorithmED25519` (lines 69-73)
+
+### Changes from original
+
+1. **GUI removed**: All Fyne GUI code stripped out
+2. **Ed25519 only**: Only Ed25519 support (original supports ECDSA/RSA too)
+3. **CLI flags**: Added flag parsing for command-line arguments
+4. **No PKCS#11**: Direct YubiKey PIV access only (no PKCS#11 smartcard support)
+5. **Simplified output**: Direct signature file write (no GUI dialogs)
+
+The core cryptographic logic is **exactly the same** as the original yubisigner. All signing functions are verbatim copies with comments indicating source line numbers.
+
+## Requirements
+
+- Go 1.21+
+- YubiKey with PIV Ed25519 key in slot 9c (Signature slot)
+- Dependencies:
+  - `github.com/go-piv/piv-go/v2/piv`
+  - `github.com/c0mm4nd/go-ripemd`
+  - `github.com/martinlindhe/gogost/gost34112012256`
+  - `github.com/tjfoc/gmsm/sm3`
+
+## Build
+
+```bash
+go build -o yubisigner-cli main.go
+```
+
+## Usage
+
+```bash
+yubisigner-cli \
+  --input <file> \
+  --author "Your Name" \
+  --email "you@example.com" \
+  --url "https://example.com" \
+  --comment "Optional comment"
+```
+
+Output: `<file>.sig` (detached signature)
+
+### Optional arguments
+
+- `--email` (default: "n/a")
+- `--url` (default: "n/a")
+- `--telefax` (default: "n/a")
+- `--comment` (default: "n/a")
+- `--pin` (PIN will be prompted if not provided)
+- `--output` (default: `<input>.sig`)
+
+## Signature format
+
+Identical to original yubisigner:
+
+```
+Author: Gab Virebent
+Signed at: 2026-05-30 23:15:00 +0000
+Filename: message.txt
+File size: 1234 bytes
+Email: gabriel1@virebent.art
+Telefax: n/a
+URL: https://contact.virebent.art
+Comment: Posted via NeoMutt mail2news
+RIPEMD-256: abc123...
+    SHA-256: def456...
+        SM3: 789abc...
+Streebog-256: fedcba...
+-----BEGIN YUBISIGNER ED25519 SIGNATURE-----
+0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+...
+-----END YUBISIGNER ED25519 SIGNATURE-----
+```
+
+## Integration with NeoMutt
+
+See [neomutt-config](https://git.virebent.art/virebent/neomutt-config) for mail2news integration with automatic YubiKey signing via the `vim-yubisigner` wrapper.
+
+## License
+
+MIT (same as original yubisigner)
+
+## Credits
+
+- **Stefan Claas** ([@Ch1ffr3punk](https://github.com/Ch1ffr3punk)): Original yubisigner GUI application
+- **Gab Virebent**: CLI extraction for automation workflows
+
+All cryptographic logic is Stefan's work. This is purely a CLI wrapper around his signing implementation.