Extracting a code signature

You can extract the DER-encoded PKCS#7 signature data from a signed file.

About this task

You can use the data found in the signature trailer to extract the DER-encoded PKCS#7 signature data from a signed file.

The following commands store the signature data:
Define the signed file as a local variable:
```
$ FILE="<file>"
```

Calculate the length, L, of the signature:

$ L=$(( $(tail -c 32 "$FILE" | hexdump -n 4 -ve '"0x%x"') ))

Use the tail command to extract the signature, located at length + 40 bytes from the end of the file, and store it a file called signature.der:
```
$ tail -c $(( L+40 )) "$FILE" > signature.der
```
Optional: Display the extracted signature.
Use the following openssl command to display the signature stored in signature.der:
```
$ openssl cms -cmsout -print -noout \
              -inform der -in signature.der
```