Use the on-line DES tool at http://des.online-domain-tools.com/ (or https://emvlab.org/descalc/) to verify that the keys (in Hex) 0101010101010101 and FEFEFEFEFEFEFEFE are weak keys. Use as input the text (in Hex) FFFFFFFFFFFFFFFF and perform encryption and then decryption obtaining identical results.

Use the ECB (Electronic Code Book) mode. The results for the key 0101010101010101 (in Hex) are (with no spaces):

for encryption ( ANSWER1 ) and for decryption ( ANSWER2 )

The results for the key FEFEFEFEFEFEFEFE (in HEX) are (again, no spaces): for encryption ( ANSWER3 ) and for decryption ( ANSWER4 )

Repeat the experiment (with the first online tool) for 3DES. Use the same plaintext (all F's in Hex) and the double-length key FEFEFEFEFEFEFEFE0101010101010101 (in Hex). The result for encryption is ( ANSWER5 ) and for decryption ( ANSWER6 )