From 63f4550d6ba28c185986488e934904c24a22b452 Mon Sep 17 00:00:00 2001
From: Omar Santos <santosomar@gmail.com>
Date: Tue, 15 Aug 2023 09:52:53 -0400
Subject: [PATCH] Create 04_Classic_Vigenere_Cipher.md

---
 .../challenges/04_Classic_Vigenere_Cipher.md  | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 crypto/challenges/04_Classic_Vigenere_Cipher.md

diff --git a/crypto/challenges/04_Classic_Vigenere_Cipher.md b/crypto/challenges/04_Classic_Vigenere_Cipher.md
new file mode 100644
index 0000000..7fe4577
--- /dev/null
+++ b/crypto/challenges/04_Classic_Vigenere_Cipher.md
@@ -0,0 +1,58 @@
+Certainly! Here are three additional cryptographic challenges suitable for your class, ranging in difficulty:
+
+### Challenge 4: Classic Vigenère Cipher
+
+**Level:** Beginner
+
+**Description:**
+Crack a message encrypted using the Vigenère cipher with a known keyword.
+
+**Challenge Text:**
+```
+Encrypted Message: "XBGXLTVJZTFKTRDCXWPNCRTGDHDDJQKFTZR"
+Keyword: "KEYWORD"
+```
+
+**Instructions:**
+1. Utilize the given keyword to decrypt the Vigenère cipher.
+2. Provide the original plaintext.
+
+### Challenge 5: Implement Diffie-Hellman Key Exchange
+
+**Level:** Intermediate
+
+**Description:**
+Simulate the Diffie-Hellman key exchange algorithm to securely share a symmetric key between two parties.
+
+**Challenge Text:**
+```
+Given prime p = 23, base g = 5
+Party A's private key: 6
+Party B's private key: 15
+```
+
+**Instructions:**
+1. Compute Party A's and Party B's public keys.
+2. Compute the shared secret key for both parties.
+3. Validate that both parties have the same shared secret key.
+
+### Challenge 6: Digital Signature Forgery
+
+**Level:** Advanced
+
+**Description:**
+Provide a digital signature scheme with a weakness (e.g., using a small prime number). Challenge the students to forge a digital signature for a new message.
+
+**Challenge Text:**
+```
+Signature scheme: RSA with n = 391, e = 3, d = 107
+Signed message: ("HELLO", signature = 220)
+Challenge: Forge a signature for the message "WORLD"
+```
+
+**Instructions:**
+1. Understand the weakness in the provided RSA signature scheme.
+2. Forge a signature for the new message.
+3. Validate the forged signature.
+
+**Note:** Make sure to clarify the educational purpose of the challenges and emphasize the importance of ethical behavior and responsible use of these skills. Providing a controlled environment or sandbox for practicing these challenges will ensure that students can learn without violating any legal or ethical guidelines.