Hot answers tagged rc4
NO. Without changing the API, it is not possible to coerce a 40-bit-key or 128-bit-key implementation of RC4 to behave like a 256-bit-key one, because there is no way to inject any key material in the RC4 state after initialization. Dave_Thompson_085 has an interesting comment for OpenSSL specifics.
Since you already know $K$, you just need to know the length of $H$ based on the hash algorithm you are using, which should be constant, then simply split the output of $D_k$ into the 2 parts of appropriate length. You can then perform the keyed hash on the first part and match it against the last part, which will match if the decryption was successful. It ...
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