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resources:rc4 [2019/11/01 16:37] jgoeders |
resources:rc4 [2019/11/01 16:39] (current) jgoeders |
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| As you may be aware, if we XOR a value with another value twice, we get back the original value (''A ^ B ^ B == A''). Thus, if we use the same key to generate the same pseudo-random stream of bytes, and XOR'd them with the cyphertext, we will get back the original plaintext. Using the same key and algorithm for encryption and decryption makes RC4 a **symmetric** encryption algorithm. This means that the provided module can be used to perform either encryption or decryption. | As you may be aware, if we XOR a value with another value twice, we get back the original value (''A ^ B ^ B == A''). Thus, if we use the same key to generate the same pseudo-random stream of bytes, and XOR'd them with the cyphertext, we will get back the original plaintext. Using the same key and algorithm for encryption and decryption makes RC4 a **symmetric** encryption algorithm. This means that the provided module can be used to perform either encryption or decryption. | ||
| - | Assuming one is using the provided module to perform RC4 decryption, the cyphertext is provided to the ''bytes_in'' input, and the key to the ''key'' input. The decryption process begins when the ''start'' signal is raised, and when completed, the ''done'' output will be high for a single cycle. The resulting plaintext is available from the ''bytes_out'' output. | + | Assuming one is using the provided module to perform RC4 decryption, the cyphertext is provided to the ''bytes_in'' input, and the key to the ''key'' input. The decryption process begins when the ''enable'' signal is raised, and when completed, the ''done'' output will be high for a single cycle. The resulting plaintext is available from the ''bytes_out'' output, which won't change until you start a new encryption/decryption process (by lower and raising the enable signal). |
| ^ Module Name = decrypt_rc4 ^^^^ | ^ Module Name = decrypt_rc4 ^^^^ | ||
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| | clk | Input | 1 | 100 MHz Clock | | | clk | Input | 1 | 100 MHz Clock | | ||
| | reset | Input | 1 | Active-high reset | | | reset | Input | 1 | Active-high reset | | ||
| - | | start | Input | 1 | Active-high, start encryption/decryption | | + | | enable| Input | 1 | Set high to start running the decryption. Once started the decryption will continue until finished. You need to lower this signal and then raise it again to start a new decryption process. | |
| | key | Input | 24 | Encryption key | | | key | Input | 24 | Encryption key | | ||
| | done | Output | 1 | Active-high for one cycle when the encryption/decryption completes| | | done | Output | 1 | Active-high for one cycle when the encryption/decryption completes| | ||
