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Derivation of SQL SERVER SP decryption process

In SQL SERVER, Microsoft is known to use the RC4 algorithm to encrypt and decrypt stored procedures. The following is the idea of decrypting the stored procedure, according to which the reader can write a decrypted Mini Program.

To decrypt SP is to answer the following proof question.

Known conditions:

1. The ciphertext of the known stored procedure SP_A that needs to be decrypted is Ma.

two。 Replace SP_A with a known plaintext SP_B, so that the plaintext and ciphertext of SP_B are Tb and Mb, respectively.

Verification: Ta=Ma ⊕ Tb ⊕ Mb,Ta is the plaintext of the stored procedure that needs to be decrypted.

Proof process:

1. Log in to SQLSERVER with DAC and get Ma and Mb: SELECT imageval FROM sys.sysobjvalues where...

two。 Since the RC4 algorithm uses the same secret key for encryption and decryption, assuming that the secret key is K, then:

A. Mb=Tb ⊕ K

b. According to the XOR formula, you can get the following secret keys used by the stored procedure to add and decrypt:

K ⊕ 0n K ⊕ Tb ⊕ Tb= (K ⊕ Tb) ⊕ Tb= (Tb ⊕ K) ⊕ Tb=Mb ⊕ Tb

3. Because of Ma=Ta ⊕ K, the following derivation results are obtained by using the XOR formula again:

Ta=Ta ⊕ 0=Ta ⊕ (K ⊕ K) = (Ta ⊕ K) ⊕ K=Ma ⊕ K=Ma ⊕ Mb ⊕ Tb

4. That is, Ta=Ma ⊕ Tb ⊕ Mb,Ta is the plaintext of the stored procedure that needs to be decrypted.

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