How to find out the encryption method

问题:

If I have the original and encrypted string how can I find out the encryption method? for example I have original string 0812388140 and the encoded one B2BCxW1tnHkzEfMfJM888Q==.

回答1:

If the encryption algorithm is secure (like any of the most supported ones is) you cannot: they are designed to make the encrypted text appear as random data, so none of them leaves a 'signature' that will hint you.

回答2:

Think about it this way: The cryptosystem is a "black box machine". You can put in a string, and you get out a string at the other end. You're not allowed to look inside. What you're asking is really how can I tell the inner workings of the black box by looking at what comes out when a single string is fed to the box? Clearly, you cannot do this.

回答3:

You cannot find-out the algorithm by simply looking at the encrypted result.