New answers tagged sha-512
No it's not. It is really bad. Basically, this is a stream cipher, where your keystream is $key | key| key|key....$. This is really bad, similar to the level of "using OTP twice". As If you take a block of size keylength, and XOR two such blocks, then you get the XOR of the plaintexts. Depending on the nature of the plaintext, this can be really easy to ...
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