Crypto

There were three questions related to cryptography which involved analysing and finiding out what kind of cipher was used to create the encoded text given to us.

The Emperor’s Secret

Ciphertext

We were provided with the following cipher text:

Jodg_brx_uhphpehu_ph

Approach

The name, the Emperor’s Secret is a big hint towards the kind of cipher it could have been, i.e. - Ceaser Cipher. However if you were unable to analyze this you can use online software like dCode cipher analyser which can help you in identifying that the cipher is indeed the Ceaser Cipher.

Once you get the cipher algorithm used, you can use a tool like dCode Cipher Decoder which can bruteforce through all possible shifts and give you the most probable answer(s).

For this question, the answer is obtained for a shift of 23. Where you get the decoded output as: Glad_you_remember_me.

The answer is therefore:

0xCTF{Glad_you_remember_me}

Nature’s Secret

Ciphertext

We were provided with the following cipher image:

Approach

The photo itself is a very big giveaway to the kind of cipher that was used. You just have to search for “Birds on a Wire Cipher” and you will get what you require.

You can use a decder from dCode.

The answer is therefore:

0xCTF{birdsonawiregochirpchirpchip}

Does size matter?

Ciphertext

We were provided with the following cipher values of an RSA encryption: Cipher text: 46163498626677786993275746470510
N(Public Key): 50537019332326445555049589372337
D(Private Key): 49623239819855508877100187645953

Approach

The approach is very straightaway in the beginning when you can directly use an RSA cipher decoder

The decrypted value is:

531095210810895110

This is where we have to start thinking different. Here we can assume that the above value is a concatenation of the ASCII values of characters.

53 109 52 108 108 95 110 = 5m4ll_n

So the answer is:

0xCTF{5m4ll_n}