encrypted_message

Encrypted Message and Signature Example

This example demonstrates how to use the message package for encrypting/decrypting messages and signing/verifying messages, leveraging ECIES and ECDSA.

Overview

The encrypted_message example (using message.go) showcases several functionalities:

1. Encryption: Encrypting a message using a sender's private key and a recipient's public key via message.Encrypt.
2. Decryption: Decrypting the ciphertext using the recipient's private key via message.Decrypt.
3. Targeted Signature: Signing a message specifically for a recipient (binding the signature to the recipient's public key) using message.Sign.
4. Targeted Verification: Verifying this targeted signature using the recipient's private key (to derive the public key for verification in the context of ECIES-like key agreement for signature verification) via message.Verify.
5. General Signature: Signing a message for general verification (not tied to a specific recipient's public key for the signature scheme itself) using message.Sign with a nil recipient public key.
6. General Verification: Verifying this general signature using message.Verify with a nil recipient (implying verification against the sender's public key directly).

Code Walkthrough

Encryption and Decryption

senderPrivKey, _ := ec.NewPrivateKey()
recipientPrivKey, _ := ec.NewPrivateKey()
messageBytes := []byte{1, 2, 4, 8, 16, 32}

// Encrypt using sender's private key and recipient's public key
encryptedData, _ := message.Encrypt(messageBytes, senderPrivKey, recipientPrivKey.PubKey())

// Decrypt using recipient's private key
// (The sender's public key is implicitly derived/used in the ECIES scheme)
decryptedData, _ := message.Decrypt(encryptedData, recipientPrivKey)
fmt.Printf("Decrypted Data: %s\n", decryptedData) // Note: %s might not be ideal for raw bytes

This part demonstrates a typical ECIES flow. message.Encrypt uses the sender's private key and recipient's public key. message.Decrypt uses the recipient's private key (the sender's public key is part of the ECIES shared secret derivation).

Targeted Message Signing and Verification

// Sign message specifically for the recipient
// This likely incorporates recipient's public key into the signing/verification process,
// possibly through a shared secret, making the signature verifiable only by the intended recipient
// or someone who can also derive that shared secret.
signatureForRecipient, _ := message.Sign(messageBytes, senderPrivKey, recipientPrivKey.PubKey())

// Verify the targeted signature using recipient's private key
// (which implies using recipient's public key in conjunction with sender's public key)
verifiedTargeted, _ := message.Verify(messageBytes, signatureForRecipient, recipientPrivKey)
fmt.Printf("Targeted signature verified: %t\n", verifiedTargeted)

Here, message.Sign with a non-nil recipient public key creates a signature that is verifiable in the context of that recipient. message.Verify uses the recipient's private key, suggesting it re-derives necessary public keys or shared secrets for this specific verification scheme.

General Message Signing and Verification

// Sign message for general verification (anyone with sender's public key can verify)
generalSignature, _ := message.Sign(messageBytes, senderPrivKey, nil) // Recipient public key is nil

// Verify the general signature
// With recipient key as nil, this likely defaults to standard ECDSA verification
// using the public key derived from senderPrivKey.
verifiedGeneral, _ := message.Verify(messageBytes, generalSignature, nil) // Assuming sender's public key is used
fmt.Printf("General signature verified: %t\n", verifiedGeneral)

This demonstrates a more standard ECDSA signature where the signature is created by the sender and can be verified by anyone who has the sender's public key. message.Verify with nil for the recipient key implies this mode.

Running the Example

To run this example:

go run message.go

The output will show the decrypted data and the verification status (true) for both targeted and general signatures.

Note:

• The message.Sign and message.Verify functions with a non-nil recipient public key implement a specific scheme. Standard ECDSA signatures don't usually involve the recipient's key directly in the signature itself but rather for encrypting a message that might contain a signature. The message package appears to offer a combined or ECIES-like approach to signed/encrypted messaging.
• For "targeted" verification, the verifier (recipient) needs their private key. For "general" verification, any party can verify using the sender's public key.

Integration Steps

For Encrypted Messaging:

1. Encrypt: message.Encrypt(payload, senderPrivKey, recipientPubKey)
2. Decrypt: message.Decrypt(encryptedPayload, recipientPrivKey)

For Targeted Signed Messaging (Recipient-Specific Verification):

1. Sign: message.Sign(payload, senderPrivKey, recipientPubKey)
2. Verify: message.Verify(payload, signature, recipientPrivKey) (Recipient verifies)

For General Signed Messaging (Public Verification):

1. Sign: message.Sign(payload, senderPrivKey, nil)
2. Verify: message.Verify(payload, signature, nil) (Anyone with sender's public key verifies; the nil here might mean the function internally uses senderPrivKey.PubKey() if the signature embeds it, or one would typically pass senderPrivKey.PubKey() if the API allowed for a public key verifier). The current API for message.Verify seems to expect a private key for the verifier argument, which it then uses to derive the necessary public key(s).

Additional Resources

For more information, see:

• Package Documentation - Message
• Package Documentation - EC primitives
• ECIES and ECDSA specifications.
• Authenticated Messaging Example (for a higher-level peer-to-peer communication)