Introduction to Cryptography

Table of Contents

Note:

The questions are shortened for a cleaner view
Questions that are straightforward will only have answers attached. Such questions can be easily answered by reading the documentation given in the room.

Task 1
#

1) You can guess that it is a quote. Who said it?
#

I used the following website to decrypt it: https://www.quipqiup.com/

“Xjnvw lc sluxjmw jsqm wjpmcqbg jg wqcxqmnvw; xjzjmmjd lc wjpm sluxjmw jsqm bqccqm zqy.” Zlwvzjxj Zpcvcol

“Today is victory over yourself of yesterday; tomorrow is your victory over lesser men.” Miyamoto Musashi

Ans: Miyamoto Musashi

Task 2 - Symmetric Encryption
#

1) Decrypt the file `quote01` encrypted (using AES256)…?
#

I’ll be using the Attackbox for this room.

Ensure you are in the right directory and run the following command:

gpg -d quote01.txt.gpg

When prompted for the passphrase, enter the given key.

gpg: AES256 encrypted data
gpg: encrypted with 1 passphrase
Do not waste time idling or thinking after you have set your goals.
Miyamoto Musashi

Ans: waste

2) Decrypt the file `quote02` encrypted (using AES256-CBC)…?
#

Run the following command:

openssl aes-256-cbc -d -in quote02

When prompted for the password, enter the given key.

*** WARNING : deprecated key derivation used.
Using -iter or -pbkdf2 would be better.
The true science of martial arts means practicing them in such a way that they will be useful at any time, and to teach them in such a way that they will be useful in all things.
Miyamoto Musashi

Ans: science

3) Decrypt the file `quote03` encrypted (using CAMELLIA256)…?
#

Run the following command:

gpg -d quote03.txt.gpg

When prompted for the passphrase, enter the given key.

gpg: CAMELLIA256 encrypted data
gpg: encrypted with 1 passphrase
You must understand that there is more than one path to the top of the mountain.
Miyamoto Musashi

Ans: understand

Task 3 - Asymmetric Encryption
#

1) What is the first word of the original plaintext?
#

Ensure you are in the right directory and run the following command:

openssl pkeyutl -decrypt -in ciphertext_message -inkey private-key-bob.pem

"Perception is strong and sight weak. In strategy it is important to see distant things as if they were close and to take a distanced view of close things."
Miyamoto Musashi

Ans: Perception

2) Take a look at Bob’s private RSA key. What is the last byte of p?
#

Run the following command:

openssl rsa -in private-key-bob.pem -text -noout

prime1:
    00:ff:ea:65:3e:e5:96:96:0b:66:55:f1:f9:d0:37:
    66:e9:35:a5:c3:43:ca:66:75:40:49:46:8d:85:a7:
    ff:f4:73:97:69:11:a1:1e:37:f9:e3:38:cb:c0:5e:
    56:e9:1a:0d:f2:9f:80:56:87:2a:99:bb:88:8e:93:
    35:5a:9a:c6:f7:99:44:90:88:09:33:a6:0d:ea:b4:
    56:98:66:20:9c:34:e7:b9:33:64:4f:08:01:08:62:
    44:68:8f:df:79:0d:84:2b:77:e7:03:8b:3c:7a:e3:
    e0:e0:ee:23:64:22:51:ed:dd:b8:1c:b3:75:c4:3f:
    4a:cf:fc:7c:57:0b:95:75:e7

The values of p, q, N, e, and d are prime1, prime2, modulus, publicExponent, and privateExponent, respectively.

Ans: e7

3) Take a look at Bob’s private RSA key. What is the last byte of q?
#

prime2:
    00:e8:72:11:5c:b5:5c:14:19:85:ce:e7:d2:e9:54:
    7b:58:ae:32:e9:e6:39:a7:65:b4:90:2f:53:b5:9d:
    22:62:84:fe:52:86:f5:01:a2:9c:b0:4f:80:ee:d4:
    07:27:3b:69:02:70:33:da:7d:97:56:b9:3e:f3:a1:
    84:9e:73:6a:47:e5:99:8c:44:86:75:c1:bf:71:89:
    06:b0:ee:dd:16:45:e7:05:fa:02:bd:e6:3e:b7:f2:
    fe:e7:22:0b:ed:ca:23:a0:68:0b:fe:fb:c3:57:19:
    21:58:6e:73:1d:9d:3c:2a:8a:c1:7e:ea:73:67:5a:
    cb:3d:a8:9b:be:50:08:9e:27

Ans: 27

Task 4 - Diffie-Hellman Key Exchange
#

1)What is the size of the prime number in bits?
#

Ensure you are in the right directory and run the following command:

openssl dhparam -in dhparams.pem -text -noout

DH Parameters: (4096 bit)
        prime:
            00:c0:10:65:c6:ad:ed:88:04:88:1e:e7:50:1b:30:
            0f:05:2c:2d:d4:ea:60:44:9e:2a:f7:90:02:89:a4:
            7e:05:99:32:38:dc:75:50:0a:c7:f6:6b:f7:b4:9a:
            df:ef:ca:e0:ce:55:5d:31:48:3e:9c:35:5a:ad:03:
            9c:87:d7:1c:48:e4:2e:29:dc:a3:90:81:23:7f:fa:
            30:5c:fb:d8:62:7b:96:35:ef:9a:0f:84:49:c4:48:
            97:b5:63:38:91:01:49:f1:42:15:fd:da:84:a6:90:
            4d:2d:05:10:41:cf:06:53:52:80:eb:1b:11:ad:5d:
            63:ed:fe:b1:f7:a7:60:1c:79:b8:88:54:a3:e4:64:
            4d:d3:04:a7:d5:76:17:00:d4:44:19:d6:12:a9:1f:
            aa:2b:ac:73:d6:52:50:92:17:a9:cd:f6:b0:ee:55:
            57:a4:db:82:6e:4f:00:20:6f:6f:f5:b1:72:97:b0:
            c5:3a:88:47:86:c6:e5:dd:fc:91:2f:82:08:05:0c:
            5c:c2:f8:62:92:67:9e:f1:53:24:c0:76:f1:3d:0c:
            50:31:5b:56:26:0a:3b:05:a3:b7:be:f9:ee:a4:82:
            f8:9d:46:ab:a9:dd:b9:04:25:61:58:aa:2a:bb:7c:
            2c:c8:e1:ef:ac:f9:50:e3:64:2e:30:9c:fd:48:26:
            25:7e:75:c0:56:58:10:8d:d7:61:b4:df:f7:ce:bd:
            9c:ef:6f:8b:47:8c:0e:cf:29:ab:eb:33:56:17:99:
            19:ee:30:5f:d9:9d:80:6e:3c:91:05:e6:cd:55:ca:
            25:f2:e3:d9:c8:68:74:1d:9e:4a:e7:53:25:1f:17:
            27:3f:4e:29:c2:19:83:da:4d:8f:b5:6b:5c:de:67:
            4f:01:10:48:84:99:32:c0:e5:e0:8b:9f:eb:4e:18:
            f7:ff:c6:47:b1:47:b8:b2:7f:3c:9c:bd:93:c2:71:
            b3:b4:37:fc:ad:2e:d9:af:2d:2c:f9:de:7f:42:8b:
            39:21:d7:47:8f:18:c4:de:ad:70:0b:11:79:c4:df:
            ef:0f:3a:9a:af:85:4e:95:05:ca:35:9e:6d:93:9b:
            e4:66:23:78:2b:d9:f4:47:e4:fe:29:1e:aa:cb:95:
            66:a2:f2:2a:c3:5a:fa:c0:a0:7d:53:bd:74:37:1d:
            b1:c7:66:67:b7:7b:5f:32:bc:2f:fa:82:0a:12:15:
            2f:41:10:cd:12:70:cc:ee:29:e7:1c:b7:07:d4:28:
            1f:73:3c:15:c0:a2:1d:2b:db:07:57:f7:10:28:c7:
            ed:e4:3a:69:c4:d9:4f:0f:c2:b4:4a:97:2a:2c:b3:
            75:77:5e:1a:21:94:8c:85:fb:0d:5e:95:0f:c8:72:
            59:6c:4f
        generator: 2 (0x2)

Ans: 4096

2)What is the prime number’s last byte (least significant byte)?
#

Ans: 4f

Task 5 - Hashing
#

1) What is the SHA256 checksum of the file `order.json`?
#

Ensure you are in the right directory and run the following command:

sha256sum order.json

2c34b68669427d15f76a1c06ab941e3e6038dacdfb9209455c87519a3ef2c660  order.json

Ans: 2c34b68669427d15f76a1c06ab941e3e6038dacdfb9209455c87519a3ef2c660

2) What is the new SHA256 checksum?
#

I used nano to edit the file. After editing, calculate the new checksum.

sha256sum order.json

11faeec5edc2a2bad82ab116bbe4df0f4bc6edd96adac7150bb4e6364a238466  order.json

Ans: 11faeec5edc2a2bad82ab116bbe4df0f4bc6edd96adac7150bb4e6364a238466

3) Using SHA256 and the key `3RfDFz82`, what is the HMAC of `order.txt`?
#

The niche tool THM was using that included commands like sha256hmac was not installed on the Attackbox for some reason so I had to use openssl instead.

Run the following command:

openssl dgst -sha256 -hmac "3RfDFz82" order.txt

HMAC-SHA256(order.txt)= c7e4de386a09ef970300243a70a444ee2a4ca62413aeaeb7097d43d2c5fac89f

Ans: c7e4de386a09ef970300243a70a444ee2a4ca62413aeaeb7097d43d2c5fac89f

Task 6 - PKI and SSL/TLS
#

1) What is the size of the public key in bits?
#

Ensure you are in the right directory and run the following command:

openssl x509 -in cert.pem  -text

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            2b:29:0c:2f:b0:52:3a:79:89:1f:82:11:07:bd:9d:84:2a:23:d5:1c
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = UK, ST = London, L = London, O = Default Company Ltd
        Validity
            Not Before: Aug 11 11:34:19 2022 GMT
            Not After : Feb 25 11:34:19 2039 GMT
        Subject: C = UK, ST = London, L = London, O = Default Company Ltd
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (4096 bit)
                Modulus: