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--- ac:laboratoare:11 [2025/11/06 10:19]
marios.choudary
+++ ac:laboratoare:11 [2025/11/06 10:36] (current)
marios.choudary
@@ Line 83: / Line 83: @@
 For this you can either modify the work you did above to use a post-quantum key exchange method such as ML-KEM in Python.
+To do this in Python you can use a library such as [[https://pypi.org/project/mlkem/|ml-kem]].
+You can install this as follows:
+<code>
+pip install ml-kem
+</code>
+Below is an example of how to use this library in a simple client-server scenario. Note: this example is provided by Gemini AI, so use it with caution and double-check it:
+<code>
+# Install the library first: pip install ml-kem
+from mlkem.ml_kem import ML_KEM
+from mlkem.parameter_set import ML_KEM_768 # Recommended security level
+import secrets
+# --- Server (Alice) Side ---
+def server_keygen():
+    """Alice generates her ML-KEM key pair."""
+    # Initialize ML-KEM with the desired security level
+    ml_kem = ML_KEM(parameters=ML_KEM_768, randomness=secrets.token_bytes)
+    # Generate the encapsulation key (ek, public) and decapsulation key (dk, private)
+    ek, dk = ml_kem.key_gen()
+    print("Alice: Generated Public Key (ek) and Private Key (dk).")
+    return ek, dk, ml_kem
+def server_decapsulate(dk, c, ml_kem):
+    """Alice decapsulates the ciphertext to get the shared secret."""
+    try:
+        K_prime = ml_kem.decaps(dk, c)
+        print("Alice: Successfully decapsulated the Shared Secret (K').")
+        return K_prime
+    except ValueError as e:
+        print(f"Alice: Decapsulation failed! {e}")
+        return None
+# --- Client (Bob) Side ---
+def client_encapsulate(ek):
+    """Bob encapsulates a shared secret using Alice's public key."""
+    ml_kem = ML_KEM(parameters=ML_KEM_768, randomness=secrets.token_bytes)
+    # Encapsulate to get the shared secret (K) and the ciphertext (c)
+    K, c = ml_kem.encaps(ek)
+    print("Bob: Encapsulated a Shared Secret (K) and created Ciphertext (c).")
+    return K, c
+# --- Communication Flow Simulation ---
+# 1. Server (Alice) Key Generation
+ek_server, dk_server, ml_kem_instance = server_keygen()
+# 2. Public Key Transmission (ek_server is sent to the client)
+print("\n--- Network Transmission: ek sent to Bob ---")
+# 3. Client (Bob) Encapsulation
+K_client, c_client = client_encapsulate(ek_server)
+# 4. Ciphertext Transmission (c_client is sent back to the server)
+print("\n--- Network Transmission: c sent to Alice ---")
+# 5. Server (Alice) Decapsulation
+K_server = server_decapsulate(dk_server, c_client, ml_kem_instance)
+# 6. Verification
+print("\n--- Verification ---")
+if K_client is not None and K_server is not None:
+    if K_client == K_server:
+        print("Success! Alice's and Bob's shared secrets match.")
+        # The shared secret can now be used as an AES key, e.g., K_client
+        # The shared secret is bytes:
+        # print(f"Shared Secret: {K_client.hex()}")
+    else:
+        print("Failure! Shared secrets do not match.")
+else:
+    print("Failure in key exchange process.")
+</code>
 Otherwise, you can start from the Diffie-Hellman key exchange lab we did in OpenSSL/C. You may start from {{:ac:laboratoare:lab_dhe_solved.zip|this}} code, that provides a working solution for the Diffie-Hellman lab in OpenSSL.
@@ Line 230: / Line 310: @@
   * Extract the raw public key bytes to replace the placeholder in the C code. A common way to get the raw bytes is to convert the PEM file to a DER format and extract the key component. For ML-KEM, the raw key is often found within the ASN.1 structure.
 <note>
-See the DH lab for information about this process
+See the DH lab for information about this process. But see also below more details for this process, as provided by Gemini AI.
 </note>
   * Compile the code (adjusting paths to your OpenSSL 3.5 installation), using a command like this (check again also the DH lab for more details):
@@ Line 236: / Line 316: @@
 gcc -o mlkem_client mlkem_client.c -I/path/to/openssl/include -L/path/to/openssl/lib -lssl -lcrypto
 </code>
+The following GeminiAI-generated scripts (might have some bugs, please double-check, they are only given as reference/helper tools) generate an ML-KEM-768 key pair and, importantly, forces OpenSSL to save the private key in the FIPS 203 'dk' format (the one the C code expects for decapsulation) rather than the default 'seed' format, which is not what the raw C code imports:
+<code>
+#!/bin/bash
+KEY_ALG="ML-KEM-768"
+PRIV_FILE="server_private_dk.pem"
+PUB_FILE="server_public_ek.pem"
+RAW_PRIV_FILE="server_private_raw.bin"
+RAW_PUB_FILE="server_public_raw.bin"
+echo "--- 1. Generating $KEY_ALG Key Pair (forcing dk-only private key) ---"
+# Generate the private key, using '-provparam ml-kem.retain_seed=no'
+# to ensure it saves the full FIPS 203 'dk' decapsulation key,
+# NOT just the seed.
+openssl genpkey -algorithm "$KEY_ALG" \
+    -provparam ml-kem.retain_seed=no \
+    -out "$PRIV_FILE"
+# Extract the public key from the private key file
+openssl pkey -in "$PRIV_FILE" -pubout -out "$PUB_FILE"
+echo "Keys generated: $PRIV_FILE and $PUB_FILE"
+echo "----------------------------------------------------------------"
+</code>
+The ML-KEM public key is in the SubjectPublicKeyInfo structure in the PEM file. We use openssl pkey to output the key in DER format and then remove the ASN.1 header/wrapper to get the raw bytes:
+<code>
+echo "--- 2. Extracting RAW Public Key (608 bytes) ---"
+# The ML-KEM public key is 608 bytes long.
+# The 'pubout' option converts to DER, and 'tail' removes the ASN.1 wrapper.
+# NOTE: The ASN.1 wrapper size may vary by OpenSSL version/config. We must
+# determine the exact offset to trim off the SubjectPublicKeyInfo header.
+# For standard ML-KEM-768 PKCS#8 output, the header is typically 24 bytes.
+HEADER_BYTES=24 # Common offset for ML-KEM-768 PKCS#8 SubjectPublicKeyInfo header
+openssl pkey -in "$PUB_FILE" -pubin -outform DER -out "$RAW_PUB_FILE"
+# Trim the ASN.1 header to get the raw 608-byte key
+# (Skip first $HEADER_BYTES, save the next 608 bytes)
+dd if="$RAW_PUB_FILE" of="client_public_key_raw_final.bin" bs=1 skip=$HEADER_BYTES count=608 status=none
+echo "Raw public key saved to client_public_key_raw_final.bin"
+# Print the hex array for C code
+echo "Public Key Hex Array:"
+xxd -p "client_public_key_raw_final.bin" | tr -d '\n' | sed 's/../&, 0x/g' | sed 's/^, 0x/0x/' | sed 's/, $//'
+echo
+echo "----------------------------------------------------------------"
+</code>
+Similarly, the private key (the FIPS 203 'dk' component) is inside the PKCS#8 private key structure. We again convert to DER and trim the ASN.1 wrappers:
+<code>
+echo "--- 3. Extracting RAW Private Key (1184 bytes) ---"
+# The ML-KEM-768 private key (dk) is 1184 bytes long.
+# We convert to DER and again skip the ASN.1 header bytes.
+# For PKCS#8 'dk' private key, the header is typically 50 bytes.
+HEADER_BYTES=50 # Common offset for ML-KEM-768 PKCS#8 PrivateKeyInfo header
+openssl pkey -in "$PRIV_FILE" -outform DER -out "$RAW_PRIV_FILE"
+# Trim the ASN.1 header to get the raw 1184-byte key
+# (Skip first $HEADER_BYTES, save the next 1184 bytes)
+dd if="$RAW_PRIV_FILE" of="server_private_key_raw_final.bin" bs=1 skip=$HEADER_BYTES count=1184 status=none
+echo "Raw private key saved to server_private_key_raw_final.bin"
+# Print the hex array for C code
+echo "Private Key Hex Array:"
+xxd -p "server_private_key_raw_final.bin" | tr -d '\n' | sed 's/../&, 0x/g' | sed 's/^, 0x/0x/' | sed 's/, $//'
+echo
+echo "----------------------------------------------------------------"
+</code>
+You can now use the hex output from these scripts to reliably replace the placeholder arrays in your C client and server code.
+See also [[https://www.youtube.com/watch?v=FzLzH5W-mi8|this]] video about Post-Quantum Cryptography support in OpenSSL.
 Below is also an example code from Gemini AI as starting point for the server, to pair with the code above for the client.

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ac/laboratoare/11.1762417149.txt.gz · Last modified: 2025/11/06 10:19 by marios.choudary

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