Add QR code generation to CLI and API

CLI generate command:
- --qr <file.png|jpg> to save RSA key as QR image
- --qr-ascii to print ASCII QR code to terminal

API endpoints:
- POST /generate-key-qr - generate QR from key_pem
  - Supports png, jpg, and ascii output formats
  - Uses zstd compression by default
- Added has_qrcode_write to /capabilities

Core:
- generate_qr_code() now supports jpg/jpeg output format
- New generate_qr_ascii() for terminal display

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

frontends/api/main.py

@@ -74,13 +74,20 @@ from stegasoo.constants import (
 try:
     from stegasoo.qr_utils import (
         extract_key_from_qr,
+        generate_qr_ascii,
+        generate_qr_code,
         has_qr_read,
+        has_qr_write,
     )
 
     HAS_QR_READ = has_qr_read()
+    HAS_QR_WRITE = has_qr_write()
 except ImportError:
     HAS_QR_READ = False
+    HAS_QR_WRITE = False
     extract_key_from_qr = None
+    generate_qr_code = None
+    generate_qr_ascii = None
 
 
 # ============================================================================
@@ -363,6 +370,7 @@ class StatusResponse(BaseModel):
     version: str
     has_argon2: bool
     has_qrcode_read: bool
+    has_qrcode_write: bool  # v4.2.0: QR generation capability
     has_dct: bool
     max_payload_kb: int
     available_modes: list[str]
@@ -378,6 +386,32 @@ class QrExtractResponse(BaseModel):
     error: str | None = None
 
 
+class QrGenerateRequest(BaseModel):
+    """Request to generate QR code from RSA key."""
+
+    key_pem: str = Field(..., description="RSA private key in PEM format")
+    output_format: str = Field(
+        default="png",
+        description="Output format: 'png', 'jpg', or 'ascii'",
+    )
+    compress: bool = Field(
+        default=True,
+        description="Compress key data with zstd (recommended for larger keys)",
+    )
+
+
+class QrGenerateResponse(BaseModel):
+    """Response containing generated QR code."""
+
+    success: bool
+    format: str | None = None
+    qr_data: str | None = Field(
+        default=None,
+        description="Base64-encoded image data (for png/jpg) or ASCII string",
+    )
+    error: str | None = None
+
+
 class WillFitRequest(BaseModel):
     """Request to check if payload will fit."""
 
@@ -496,6 +530,7 @@ async def root():
         version=__version__,
         has_argon2=has_argon2(),
         has_qrcode_read=HAS_QR_READ,
+        has_qrcode_write=HAS_QR_WRITE,
         has_dct=has_dct_support(),
         max_payload_kb=MAX_FILE_PAYLOAD_SIZE // 1024,
         available_modes=available_modes,
@@ -787,6 +822,51 @@ async def api_extract_key_from_qr(
         return QrExtractResponse(success=False, error=str(e))
 
 
+@app.post("/generate-key-qr", response_model=QrGenerateResponse)
+async def api_generate_key_qr(request: QrGenerateRequest):
+    """
+    Generate QR code from an RSA private key.
+
+    Supports PNG, JPG, and ASCII output formats.
+    Uses zstd compression by default for better QR code density.
+    """
+    if not HAS_QR_WRITE:
+        raise HTTPException(501, "QR code generation not available. Install qrcode library.")
+
+    try:
+        fmt = request.output_format.lower()
+
+        if fmt == "ascii":
+            ascii_qr = generate_qr_ascii(
+                request.key_pem,
+                compress=request.compress,
+                invert=False,
+            )
+            return QrGenerateResponse(success=True, format="ascii", qr_data=ascii_qr)
+
+        elif fmt in ("png", "jpg", "jpeg"):
+            import base64
+
+            qr_bytes = generate_qr_code(
+                request.key_pem,
+                compress=request.compress,
+                output_format=fmt,
+            )
+            qr_b64 = base64.b64encode(qr_bytes).decode("ascii")
+            return QrGenerateResponse(success=True, format=fmt, qr_data=qr_b64)
+
+        else:
+            return QrGenerateResponse(
+                success=False,
+                error=f"Unsupported format: {fmt}. Use 'png', 'jpg', or 'ascii'",
+            )
+
+    except ValueError as e:
+        return QrGenerateResponse(success=False, error=str(e))
+    except Exception as e:
+        return QrGenerateResponse(success=False, error=f"QR generation failed: {e}")
+
+
 # ============================================================================
 # ROUTES - GENERATE
 # ============================================================================

frontends/cli/main.py

@@ -120,6 +120,7 @@ try:
     from stegasoo.qr_utils import (  # noqa: F401
         can_fit_in_qr,
         extract_key_from_qr_file,
+        generate_qr_ascii,
         generate_qr_code,
         has_qr_read,
         has_qr_write,
@@ -136,6 +137,9 @@ except ImportError:
     def has_qr_write() -> bool:
         return False
 
+    def generate_qr_ascii(*args, **kwargs):
+        raise RuntimeError("QR code generation not available")
+
 
 # ============================================================================
 # CLI SETUP
@@ -247,7 +251,13 @@ def format_channel_status_line(quiet: bool = False) -> str | None:
 @click.option("--output", "-o", type=click.Path(), help="Save RSA key to file (requires password)")
 @click.option("--password", "-p", help="Password for RSA key file")
 @click.option("--json", "as_json", is_flag=True, help="Output as JSON")
-def generate(pin, rsa, pin_length, rsa_bits, words, output, password, as_json):
+@click.option(
+    "--qr",
+    type=click.Path(),
+    help="Save RSA key QR code to file (png/jpg, uses zstd compression)",
+)
+@click.option("--qr-ascii", is_flag=True, help="Print RSA key as ASCII QR code to terminal")
+def generate(pin, rsa, pin_length, rsa_bits, words, output, password, as_json, qr, qr_ascii):
     """
     Generate credentials for encoding/decoding.
 
@@ -263,11 +273,16 @@ def generate(pin, rsa, pin_length, rsa_bits, words, output, password, as_json):
         stegasoo generate --words 5
         stegasoo generate --rsa --rsa-bits 3072
         stegasoo generate --rsa -o mykey.pem -p "secretpassword"
+        stegasoo generate --rsa --qr key.png
+        stegasoo generate --rsa --qr-ascii
         stegasoo generate --no-pin --rsa
     """
     if not pin and not rsa:
         raise click.UsageError("Must enable at least one of --pin or --rsa")
 
+    if (qr or qr_ascii) and not rsa:
+        raise click.UsageError("QR output requires --rsa to generate an RSA key")
+
     if output and not password:
         raise click.UsageError("--password is required when saving RSA key to file")
 
@@ -334,6 +349,33 @@ def generate(pin, rsa, pin_length, rsa_bits, words, output, password, as_json):
                 click.echo(creds.rsa_key_pem)
             click.echo()
 
+            # QR code output (v4.2.0)
+            if qr:
+                if not HAS_QR:
+                    click.secho("    ⚠️  QR code library not available", fg="yellow")
+                else:
+                    # Determine format from extension
+                    qr_path = Path(qr)
+                    ext = qr_path.suffix.lower()
+                    fmt = "jpeg" if ext in (".jpg", ".jpeg") else "png"
+
+                    qr_bytes = generate_qr_code(creds.rsa_key_pem, compress=True, output_format=fmt)
+                    qr_path.write_bytes(qr_bytes)
+                    click.secho(f"─── RSA KEY QR CODE ───", fg="green")
+                    click.secho(f"    Saved to: {qr}", fg="bright_white")
+                    click.secho("    ⚠️  Contains unencrypted private key!", fg="yellow")
+                    click.echo()
+
+            if qr_ascii:
+                if not HAS_QR:
+                    click.secho("    ⚠️  QR code library not available", fg="yellow")
+                else:
+                    click.secho("─── RSA KEY QR CODE (ASCII) ───", fg="green")
+                    click.secho("    ⚠️  Contains unencrypted private key!", fg="yellow")
+                    click.echo()
+                    ascii_qr = generate_qr_ascii(creds.rsa_key_pem, compress=True, invert=True)
+                    click.echo(ascii_qr)
+
         click.secho("─── SECURITY ───", fg="green")
         click.echo(f"    Passphrase entropy: {creds.passphrase_entropy} bits ({words} words)")
         if creds.pin:

src/stegasoo/qr_utils.py

@@ -252,17 +252,23 @@ def needs_compression(data: str) -> bool:
     return not can_fit_in_qr(data, compress=False) and can_fit_in_qr(data, compress=True)
 
 
-def generate_qr_code(data: str, compress: bool = False, error_correction=None) -> bytes:
+def generate_qr_code(
+    data: str,
+    compress: bool = False,
+    error_correction=None,
+    output_format: str = "png",
+) -> bytes:
     """
-    Generate a QR code PNG from string data.
+    Generate a QR code image from string data.
 
     Args:
         data: String data to encode
         compress: Whether to compress data first
         error_correction: QR error correction level (default: auto)
+        output_format: Image format - 'png' or 'jpg'/'jpeg'
 
     Returns:
-        PNG image bytes
+        Image bytes in requested format
 
     Raises:
         RuntimeError: If qrcode library not available
@@ -299,11 +305,79 @@ def generate_qr_code(data: str, compress: bool = False, error_correction=None) -
     img = qr.make_image(fill_color="black", back_color="white")
 
     buf = io.BytesIO()
+    fmt = output_format.lower()
+    if fmt in ("jpg", "jpeg"):
+        # Convert to RGB for JPEG (no alpha channel)
+        img = img.convert("RGB")
+        img.save(buf, format="JPEG", quality=95)
+    else:
         img.save(buf, format="PNG")
     buf.seek(0)
     return buf.getvalue()
 
 
+def generate_qr_ascii(
+    data: str,
+    compress: bool = False,
+    invert: bool = False,
+) -> str:
+    """
+    Generate an ASCII representation of a QR code.
+
+    Uses Unicode block characters for compact display.
+
+    Args:
+        data: String data to encode
+        compress: Whether to compress data first
+        invert: Invert colors (white on black for dark terminals)
+
+    Returns:
+        ASCII string representation of QR code
+
+    Raises:
+        RuntimeError: If qrcode library not available
+        ValueError: If data too large for QR code
+    """
+    if not HAS_QRCODE_WRITE:
+        raise RuntimeError("qrcode library not installed. Run: pip install qrcode[pil]")
+
+    qr_data = data
+
+    # Compress if requested
+    if compress:
+        qr_data = compress_data(data)
+
+    # Check size
+    if len(qr_data.encode("utf-8")) > QR_MAX_BINARY:
+        raise ValueError(
+            f"Data too large for QR code ({len(qr_data)} bytes). " f"Maximum: {QR_MAX_BINARY} bytes"
+        )
+
+    qr = qrcode.QRCode(
+        version=None,
+        error_correction=ERROR_CORRECT_L,
+        box_size=1,
+        border=2,
+    )
+    qr.add_data(qr_data)
+    qr.make(fit=True)
+
+    # Get the QR matrix
+    # Use print_ascii to a StringIO to capture output
+    import sys
+    from io import StringIO
+
+    old_stdout = sys.stdout
+    sys.stdout = StringIO()
+    try:
+        qr.print_ascii(invert=invert)
+        ascii_qr = sys.stdout.getvalue()
+    finally:
+        sys.stdout = old_stdout
+
+    return ascii_qr
+
+
 def read_qr_code(image_data: bytes) -> str | None:
     """
     Read QR code from image data.