#!/bin/sh

# Exit immediately if a command exits with a non-zero status
set -e

# Summary of the script's functionality
summary="Decrypts a JWE using a TPM2.0 chip."

# TPM2.0 owner hierarchy to be used by the Operating System
auth="o"

# Display summary if requested
if [ "$1" = "--summary" ]; then
    echo "$summary"
    exit 0
fi

# Display usage information if input is from a terminal
if [ -t 0 ]; then
    exec >&2
    echo
    echo "Usage: \"zlevis-decrypt < file.jwe\""
    echo "Usage ZFS: \"zfs list -Ho tpm:jwe <pool> | zlevis-decrypt\""
    echo
    echo "$summary"
    exit 2
fi

# Function to clean up temporary files on exit
on_exit() {
    if [ ! -d "$tmp" ] || ! rm -rf "$tmp"; then
        echo "Delete temporary files failed" >&2
        echo "You need to clean up: $tmp" >&2
        exit 1
    fi
}

# Get the version of tpm2-tools
tpm2tools_version=$(tpm2_createprimary -v | awk -F'version="' '{print $2}' | awk -F'.' '{print $1}')

# Check if the tpm2-tools version is supported
if [ -z "$tpm2tools_version" ] || [ "$tpm2tools_version" -lt 4 ] || [ "$tpm2tools_version" -gt 5 ]; then
    echo "The tpm2 pin requires a tpm2-tools version between 4 and 5"
    exit 1
fi

# Create a temporary directory for TPM files
if ! tmp="$(mktemp -d)"; then
    echo "Creating a temporary dir for TPM files failed" >&2
    exit 1
fi

# Set up cleanup on exit
trap 'on_exit' EXIT

# Read the JWE protected header
read -r -d . hdr
echo "$hdr" > "$tmp"/hdr

# Decode the JWE protected header
if ! jhd="$(jose b64 dec -i- < "$tmp"/hdr)"; then
    echo "Error decoding JWE protected header" >&2
    exit 1
fi
echo "$jhd" > "$tmp"/jhd

# Validate the JWE pin type
if [ "$(jose fmt -j- -Og clevis -g pin -u- < "$tmp"/jhd)" != "tpm2" ]; then
    echo "JWE pin mismatch" >&2
    exit 1
fi

# Extract required parameters from the JWE header
if ! hash="$(jose fmt -j- -Og clevis -g tpm2 -g hash -Su- < "$tmp"/jhd)"; then
    echo "JWE missing required 'hash' header parameter!" >&2
    exit 1
fi
if ! key="$(jose fmt -j- -Og clevis -g tpm2 -g key -Su- < "$tmp"/jhd)"; then
    echo "JWE missing required 'key' header parameter!" >&2
    exit 1
fi
if ! jwk_pub="$(jose fmt -j- -Og clevis -g tpm2 -g jwk_pub -Su- < "$tmp"/jhd)"; then
    echo "JWE missing required 'jwk_pub' header parameter!" >&2
    exit 1
fi
echo "$jwk_pub" > "$tmp"/jwk_pub
if ! jwk_priv="$(jose fmt -j- -Og clevis -g tpm2 -g jwk_priv -Su- < "$tmp"/jhd)"; then
    echo "JWE missing required 'jwk_priv' header parameter!" >&2
    exit 1
fi
echo "$jwk_priv" > "$tmp"/jwk_priv

# Handle optional PCR parameters
pcr_ids="$(jose fmt -j- -Og clevis -g tpm2 -g pcr_ids -Su- < "$tmp"/jhd)" || true
pcr_spec=""
if [ -n "$pcr_ids" ]; then
    pcr_bank="$(jose fmt -j- -Og clevis -g tpm2 -g pcr_bank -Su- < "$tmp"/jhd)"
    pcr_spec="$pcr_bank:$pcr_ids"
fi

# Decode the public and private keys from Base64
if ! jose b64 dec -i- -O "$tmp"/jwk.pub < "$tmp"/jwk_pub; then
    echo "Decoding jwk.pub from Base64 failed" >&2
    exit 1
fi
if ! jose b64 dec -i- -O "$tmp"/jwk.priv < "$tmp"/jwk_priv; then
    echo "Decoding jwk.priv from Base64 failed" >&2
    exit 1
fi

# Create the primary key in the TPM
case "$tpm2tools_version" in
    4|5) tpm2_createprimary -Q -C "$auth" -g "$hash" -G "$key" -c "$tmp"/primary.context || fail=$?;;
    *) fail=1;;
esac
if [ -n "$fail" ]; then
    echo "Creating TPM2 primary key failed" >&2
    exit 1
fi
tpm2_flushcontext -t

# Load the JWK into the TPM
case "$tpm2tools_version" in
    4|5) tpm2_load -Q -C "$tmp"/primary.context -u "$tmp"/jwk.pub -r "$tmp"/jwk.priv -c "$tmp"/load.context || fail=$?;;
    *) fail=1;;
esac
if [ -n "$fail" ]; then
    echo "Loading jwk to TPM2 failed" >&2
    exit 1
fi
tpm2_flushcontext -t

# Unseal the JWK from the TPM
case "$tpm2tools_version" in
    4|5) jwk="$(tpm2_unseal -c "$tmp/load.context" ${pcr_spec:+-p pcr:$pcr_spec})" || fail=$?;;
    *) fail=1;;
esac
if [ -n "$fail" ]; then
    echo "Unsealing jwk from TPM failed" >&2
    exit 1
fi
tpm2_flushcontext -t

# Output the decrypted JWK along with the original header
(echo "$jwk$hdr."; /bin/cat) | jose jwe dec -k- -i-

# Exit with the status of the last command
exit $?