How can I encrypt a 300-bit plaintext using a block cipher with a block size of 128 bits in ECB mode?

First you have do some padding. The most simple padding would be to fill your plaintext with zeros up to size 3*128 bits. Now you can encrypt it with your block cipher in three steps, first encrypting bits 0 to 127, then 128 to 255 and last 256 to 383.

That's ECB.

First you have do some padding. The most simple padding would be to fill your plaintext with zeros up to size 3*128 bits. Now you can encrypt it with your block cipher in three steps, first encrypting bits 0 to 127, then 128 to 255 and last 256 to 383.

That's ECB. For decryption you do the reverse. Decrypt the single blocks, then remove the padding.

I would say that using ECB for len(cleartext) > block size is not recommended. If you can live with ciphertext expansion due to padding on the last block then you can do as tangens recommends. If you need the len(ciphertext) == len(cleartext) you need to look at cipherhext stealing versions of ECB (or CBC): en.wikipedia.org/wiki/Ciphertext_stealing csrc.nist.gov/publications/nistpubs/800-....

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.