December 2025
Daily Cryptography Challenges
31 Days • 31 Ciphers
31 days of cryptography challenges to master cipher-breaking this December
New cryptography challenges unlock each day throughout December. Decrypt the ciphers and submit your flags!
In 58 BC, Julius Caesar encrypted his military communications using a substitution cipher. Your mission: intercept and decrypt an encoded message from his campaign in Gaul. The cipher shifts each letter by a fixed number of positions in the alphabet. Intelligence suggests the shift value is 3.
A spy has sent you an urgent message, but it appears scrambled. Upon closer inspection, you realize the text has been reversed—a technique used by ancient Greek cryptographers. Your task is to restore the message to its original form and reveal the hidden intelligence.
You've intercepted a data transmission from an unknown source. The message appears to be encoded in Base64—a binary-to-text encoding scheme commonly used to safely transmit data across networks. Decode this transmission to uncover the flag hidden within the seemingly random string of characters.
A double agent has delivered an encrypted hex string. Intelligence reports suggest it was encrypted using the XOR (exclusive OR) cipher with a single repeating byte as the key. XOR encryption is symmetric—the same key both encrypts and decrypts. Your mission: brute force the key space (0-255) to reveal the secret.
You've breached a secure vault and discovered a message protected by the Vigenère cipher—a polyalphabetic substitution cipher once considered 'le chiffre indéchiffrable' (the indecipherable cipher). Unlike Caesar's simple shift, Vigenère uses a keyword to shift each letter by different amounts. The keyword has been compromised: 'CIPHER'. Decrypt the vault's contents before time runs out.
[REDACTED] This classified cryptography challenge will be declassified on December 6th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 7th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 8th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 9th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 10th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 11th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 12th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 13th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 14th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 15th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 16th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 17th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 18th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 19th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 20th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 21th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 22th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 23th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 24th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 25th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 26th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 27th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 28th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 29th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 30th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.
[REDACTED] This classified cryptography challenge will be declassified on December 31th. Prepare your cipher-breaking tools and analytical skills for what lies ahead.