mrs-smime.sh

#!/bin/bash

if [ "$1" = '-h' ] || [ "$1" = '--help' ]; then { echo "This script is meant to be run interactively without arguments."; exit 0; } fi


#Prompt user to select email.
# Leveraging applescript for prompts
echo "Prompting user for p7m file..."
p7mFile=$(osascript -e 'tell application (path to frontmost application as text)
set myFile to choose file of type {"dyn.ah62d4rv4ge81ar5r"} with prompt "Select p7m file to decrypt"
POSIX path of myFile
end')
if [ $? -ne 0 ]; then { echo 'p7m file was not selected' ; exit 1; } fi
echo $p7mFile
# The strange file type was determined by running the command:
#  osascript -e 'info for "./smime.p7m"'


echo "Prompting user for output folder..."
outFolder=$(osascript -e 'tell application (path to frontmost application as text)
set outFolder to choose folder with prompt "Please select or create a folder to store the output:"
POSIX path of outFolder
end')
if [ $? -ne 0 ]; then { echo 'Output folder was not selected' ; exit 1; } fi
echo $outFolder


echo "Decrypting file ..."
decrypted="$outFolder/decrypted.smime"

# - Decrypts file using native mac stuff
security cms -D -i "$p7mFile" \
  > $decrypted

if [ $? -ne 0 ] ; then {
  echo 'Failed to decrypt file'; 
  exit 1;
} fi

decoded="$outFolder/decoded.smime"
# check to see if file is already decoded

final=$decrypted
# - Removes MIME headers (sed: delete (/d) all lines from line 1 to pattern: line with nothing in it)
# - Removes new lines 
# - Decodes out of base 64 
# - Takes out everything before "MIME-Version" (the signature bytes) on the first line
# - Same but for Conent-Type on first line
# - Outputs to 'decrypted.smime' in the selected output folder
if !  grep -q 'Content-Type: text/plain' $decrypted; then {
  echo "Decoding multi-part smime file..."
  cat $decrypted \
  | sed '1,/^\s*\r$/d' \
  | sed 's/\r$//' \
  | base64 --decode \
  | perl -pe '$. == 1? s/^.*(MIME-Version: [\d\.]+)/$1/ : "" ' \
  | perl -pe '$. == 1? s/^.*(Content-Type: .+)/$1/ : "" ' \
  > $decoded
  final=$decoded
} fi

if [ $? -ne 0 ]  ; then { echo 'Failed to decode file (first pass)' ; exit 1; } fi


echo "Decoding file..."
python3 "$(dirname $0)/mimesplit.py" -d "$outFolder" "$final"
if [ $? -ne 0 ] ; then { echo 'Failed to decode file (second pass)' ; exit 1; } fi

echo "Script complete. Files located at '$outFolder'"