S7-PLC_SHA1

SHA1 encryption FC for Siemens PLC S7-1200 and S7-1500

Sha1 is an cryptographic algorithm that takes a string of any length and reduces it to a unique fixed length string. In this implmementation the string length is limited to a maximum length of 254 characters (String[254] - 2032 bit).

depending on the input “inputmode” different inputformats are used

- 1 Message is used as Bytes
- 2 Message is used as String

depending on the input “outputmode” different outputformats are available

-1 The digest ouput is the final hash value as a string of H0 - H4 (Array [0..19] of Byte)
-2 The hexdigest output is the final hash value as a hexadecimal string of H0 - H4 (40 bytes string)
-3 Both 1 and 2

For further informations take a look at RFC 3174. Sha1 is not considered anymore as a secure hash type!

steps:

-Step 00: Initialize variables H0 - H4
-Step 01: Convert message to Bytes
-Step 02: Appending padding Bits
-Step 03: Append 64 Bit containg the original message length in Bits
-Step 04: Get the amount of chunks data (chunk = 512 Bit)
-FOR every chunk do Step 05 - Step 09:
    -Step 05: Break the chunk into 16 DWords
    -Step 06: Extend chunk to 80 DWords
    -Step 07: Initialize variables A - E
    -Step 08: Do some bitwise operations on the 80 chunk DWords
    -Step 09: Save the chunk's hash to result for the next chunk
-Step 10: Produce "digest"
-Step 11: Produce "hexdigest"