Function Reference

1. GenerateKeyPair()

Generates a public/private key pair for a user.

Output: publicKey & privateKey (Base64)

2. EstablishSharedKey(myPrivateKey, otherPublicKey)

Derives a shared session key.

Output: SharedSessionKey (Base64)

3. EncryptMessage(sessionKey, plaintext)

Encrypts a plaintext string using AES-256-GCM.

Output: ciphertext & iv (Base64)

4. DecryptMessage(sessionKey, ciphertext, iv)

Decrypts ciphertext back into plaintext.

Output: PlainText (String)

Integration Flow

GenerateKeyPair() – Both sender and receiver create their key pairs.

Exchange Public Keys – Share only public keys.

EstablishSharedKey() – Derive a shared session key.

EncryptMessage() – Encrypt messages using the session key.

DecryptMessage() – Decrypt received messages.

Flow of the Project

Step 1: Generate Key Pair for Sender

• Function: GenerateKeyPair()
• What it does:
  Creates a public/private key pair for the sender using ECDH (Elliptic Curve Diffie-Hellman).
• Why:
  This identifies the sender and enables secure key exchange later.
• Output:
  • PublicKeyOfSender (Base64) → Can be shared with others.
  • PrivateKeyOfSender (Base64) → Must be kept secret.

Step 2: Generate Key Pair for Receiver

• Function: GenerateKeyPair()
• What it does:
  Creates a public/private key pair for the receiver using the same algorithm.
• Why:
  The receiver also needs their own keys for secure key exchange.
• Output:
  • PublicKeyOfReceiver (Base64).
  • PrivateKeyOfReceiver (Base64).

Step 3: Establish Shared Session Key

• Function: EstablishSharedKey(PrivateKeyOfSender, PublicKeyOfReceiver)
• What it does:
  Uses ECDH to derive a shared session key using:
  • The sender’s private key.
  • The receiver’s public key.
• Why:
  Both parties end up with the same session key without ever transmitting it directly.
• Output:
  • SharedSessionKey (Base64) → Used for encrypting/decrypting messages.

(The receiver can also run EstablishSharedKey(PrivateKeyOfReceiver, PublicKeyOfSender) to get the same session key.)

Step 4: Encrypt a Message

• Function: EncryptMessage(SharedSessionKey, PlainText)
• What it does:
  Encrypts the plaintext message using AES-256-GCM with the session key.
• Why:
  Protects the message contents (confidentiality) and ensures integrity (no tampering).
• Output:
  • Ciphertext (Base64) → The encrypted message.
  • IV (Base64) → Random initialization vector used for encryption.

Step 5: Decrypt a Message

• Function: DecryptMessage(SharedSessionKey, Ciphertext, IV)
• What it does:
  Decrypts the ciphertext using AES-256-GCM with the shared session key and IV.
• Why:
  Allows the receiver to recover the original message securely.
• Output:
  • PlainText → The decrypted readable message.