skel/bin/ssh-sign

#!/bin/bash
# A robust wrapper for ssh-keygen to sign and verify files.

# --- Color Codes for Output ---
COLOR_RED='\033[0;31m'
COLOR_GREEN='\033[0;32m'
COLOR_NONE='\033[0m' # No Color

# --- Default values ---
DEFAULT_SIGNING_KEY="$HOME/.ssh/id_signing"
DEFAULT_ALLOWED_SIGNERS="$HOME/.ssh/allowed_signers"
DEFAULT_IDENTITY="david@systemoverlord.com"
DEFAULT_NAMESPACE="file"

# --- Usage Message ---
usage() {
  cat << EOF
Usage: $(basename "$0") <sign|verify> [OPTIONS] [FILE]

A wrapper for 'ssh-keygen -Y' to simplify file signing and verification.

COMMANDS:
  sign      Sign a file. The path to the file to be signed is provided as a positional argument.
  verify    Verify a signature. The original file content is read from stdin.

OPTIONS:
  -f <file>         For 'sign': Path to the private key for signing.
                    Defaults to '$DEFAULT_SIGNING_KEY' if it exists.
                    For 'verify': Path to the allowed_signers file.
                    Defaults to '$DEFAULT_ALLOWED_SIGNERS'.
  -n <namespace>    Signature namespace.
                    Defaults to '$DEFAULT_NAMESPACE'.
  -I <identity>     For 'verify': The identity to check the signature against.
                    Defaults to '$DEFAULT_IDENTITY'.
  -s <sig_file>     For 'verify': Path to the signature file to verify (e.g., file.sig). REQUIRED for verify.
  -h, --help        Show this help message.

EXAMPLE USAGE:
  # Sign a file using the default key
  $(basename "$0") sign release.tar.gz

  # Sign a file with a specific key
  $(basename "$0") sign -f ~/.ssh/id_ed25519_my_signing_key release.tar.gz

  # Verify a signature using default allowed_signers and identity
  cat release.tar.gz | $(basename "$0") verify -s release.tar.gz.sig

  # Verify a signature with a specific allowed_signers file and identity
  cat release.tar.gz | $(basename "$0") verify -f ./my_signers -I other@example.com -s release.tar.gz.sig

EOF
  exit 1
}

# --- Helper for error messages ---
error() {
  echo -e "${COLOR_RED}Error: $1${COLOR_NONE}" >&2
  exit 1
}

# --- Main Script Logic ---

if [[ "$1" != "sign" && "$1" != "verify" ]]; then
  usage
fi

SUBCOMMAND=$1
shift # Consume the subcommand

# --- Argument Parsing and Validation ---

# Separate arguments from the file to be signed
declare -a remaining_args
file_to_sign=""
while [[ "$#" -gt 0 ]]; do
  # If we see a non-flag argument, assume it's the file to sign.
  # This works because the file to sign is the only positional argument.
  if [[ "$1" != -* ]] && [[ -z "$file_to_sign" ]]; then
    file_to_sign="$1"
  else
    remaining_args+=("$1")
  fi
  shift
done

# --- Build command based on subcommand ---
declare -a CMD_ARGS
CMD_ARGS=("ssh-keygen" "-Y" "$SUBCOMMAND")

# Append all the flag-based arguments (-f, -n, -I, -s)
CMD_ARGS+=("${remaining_args[@]}")

# Scan for provided flags to handle defaults correctly
f_provided=false
n_provided=false
I_provided=false
s_provided=false
for arg in "${remaining_args[@]}"; do
  [[ "$arg" == "-f" ]] && f_provided=true
  [[ "$arg" == "-n" ]] && n_provided=true
  [[ "$arg" == "-I" ]] && I_provided=true
  [[ "$arg" == "-s" ]] && s_provided=true
done

if [[ "$SUBCOMMAND" == "sign" ]]; then
  if [[ -z "$file_to_sign" ]]; then
    error "Path to file to be signed is required for 'sign' command."
  fi
  
  # Set default signing key if -f was not provided
  if ! $f_provided; then
    if [[ ! -f "$DEFAULT_SIGNING_KEY" ]]; then
      error "Default signing key not found at '$DEFAULT_SIGNING_KEY'. Specify one with -f."
    fi
    CMD_ARGS+=("-f" "$DEFAULT_SIGNING_KEY")
  fi
  
  # Set default namespace if -n was not provided
  if ! $n_provided; then
    CMD_ARGS+=("-n" "$DEFAULT_NAMESPACE")
  fi
  
  # The file to sign MUST be the last argument for ssh-keygen
  CMD_ARGS+=("$file_to_sign")

elif [[ "$SUBCOMMAND" == "verify" ]]; then
  if [[ -n "$file_to_sign" ]]; then
    error "The 'verify' command reads from stdin and does not accept a positional file argument. Found '$file_to_sign'."
  fi
  if ! $s_provided; then
    error "Signature file must be provided with -s for 'verify' command."
  fi
  
  # Set default allowed_signers if -f was not provided
  if ! $f_provided; then
    if [[ ! -f "$DEFAULT_ALLOWED_SIGNERS" ]]; then
      error "Default allowed signers file not found at '$DEFAULT_ALLOWED_SIGNERS'. Specify one with -f."
    fi
    CMD_ARGS+=("-f" "$DEFAULT_ALLOWED_SIGNERS")
  fi
  
  # Set default identity if -I was not provided
  if ! $I_provided; then
    CMD_ARGS+=("-I" "$DEFAULT_IDENTITY")
  fi
  
  # Set default namespace if -n was not provided
  if ! $n_provided; then
    CMD_ARGS+=("-n" "$DEFAULT_NAMESPACE")
  fi
fi

# --- Execute and Report ---

# We capture the output and stderr to show it to the user
if output=$("${CMD_ARGS[@]}" 2>&1); then
  echo -e "${COLOR_GREEN}Success:${COLOR_NONE}"
  echo "$output"
  exit 0
else
  echo -e "${COLOR_RED}Command Failed:${COLOR_NONE}"
  echo "$output" >&2
  exit 1
fi