Initial commit: SecPaste encrypted pastebin client

SecPaste is a Python library and CLI tool for sharing encrypted content via
public pastebin services with zero-knowledge architecture.

Features:
- Pluggable crypto backends (AES-256-GCM, ChaCha20-Poly1305, Kyber-768)
- Pluggable pastebin providers (dpaste.com, extensible)
- URL fragment key storage (key never sent to server)
- Both CLI and library usage
- Post-quantum cryptography support (experimental)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

providers/dpaste.py

@@ -0,0 +1,103 @@
+"""dpaste.com provider implementation."""
+
+import base64
+import requests
+from typing import Optional
+from .base import PastebinProvider
+
+
+class DPasteProvider(PastebinProvider):
+    """Provider for dpaste.com pastebin service."""
+
+    BASE_URL = "https://dpaste.com"
+
+    def __init__(self, api_url: Optional[str] = None):
+        """
+        Initialize dpaste provider.
+
+        Args:
+            api_url: Override API URL (useful for self-hosted instances)
+        """
+        self.api_url = api_url or self.BASE_URL
+
+    def paste(self, content: bytes, expiry: str = "onetime", syntax: str = "text", **kwargs) -> str:
+        """
+        Upload encrypted content to dpaste.
+
+        Args:
+            content: Encrypted bytes to upload
+            expiry: Expiration time (onetime, hour, day, week, month, never)
+            syntax: Syntax highlighting (text, python, etc.)
+            **kwargs: Additional provider-specific options
+
+        Returns:
+            Full paste URL (without fragment)
+        """
+        # Base64 encode binary content for safe transmission
+        content_b64 = base64.b64encode(content).decode('ascii')
+
+        # dpaste API expects form data
+        data = {
+            'content': content_b64,
+            'syntax': syntax,
+            'expiry_days': self._convert_expiry(expiry),
+        }
+
+        # POST to create paste
+        response = requests.post(
+            f"{self.api_url}/api/v2/",
+            data=data,
+            headers={'User-Agent': 'SecPaste/0.1.0'}
+        )
+        response.raise_for_status()
+
+        # dpaste returns plain text URL
+        paste_url = response.text.strip()
+        return paste_url
+
+    def fetch(self, paste_id: str) -> bytes:
+        """
+        Fetch encrypted content from dpaste.
+
+        Args:
+            paste_id: Full URL or just the paste ID
+
+        Returns:
+            Encrypted bytes (base64 decoded)
+        """
+        # Handle both full URLs and just IDs
+        if paste_id.startswith('http'):
+            url = paste_id
+        else:
+            url = f"{self.api_url}/{paste_id}"
+
+        # Add .raw to get raw content
+        if not url.endswith('.raw'):
+            url = f"{url}.raw"
+
+        response = requests.get(url, headers={'User-Agent': 'SecPaste/0.1.0'})
+        response.raise_for_status()
+
+        # Decode from base64
+        content = base64.b64decode(response.text.strip())
+        return content
+
+    def get_name(self) -> str:
+        """Return provider name."""
+        return "dpaste"
+
+    def get_base_url(self) -> str:
+        """Return base URL."""
+        return self.api_url
+
+    def _convert_expiry(self, expiry: str) -> str:
+        """Convert expiry string to dpaste format."""
+        expiry_map = {
+            'onetime': '0',
+            'hour': '1',
+            'day': '1',
+            'week': '7',
+            'month': '30',
+            'never': '365'  # dpaste max is 365 days
+        }
+        return expiry_map.get(expiry, '7')