KyberDecapsulate()

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Recovers the shared secret from a Kyber ciphertext using your private key.

This is the recipient's side of a Kyber key exchange — the shared secret matches what the sender got from KyberEncapsulate().

Requires Extension: Crypto Extension

KyberDecapsulate( privateKey=any, ciphertext=string );

Returns: binary

Argument Description
privateKey
any, required 		edit

Kyber private key (PEM string or Java object)
ciphertext
string, required 		edit

Base64-encoded ciphertext from KyberEncapsulate

Usage Notes

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Implicit rejection: If you decapsulate with the wrong private key, you get a different (incorrect) shared secret rather than an error. This is a deliberate security feature of the Kyber specification — it prevents an attacker from learning whether a ciphertext is valid. Your application should detect the mismatch at a higher level (e.g. AES decryption will fail with the wrong key).

Examples

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// Decapsulate a Kyber ciphertext to recover the shared secret
// This is the recipient's side of the Kyber key exchange

// Recipient's key pair (private key must be kept secret)
keys = GenerateKeyPair( "Kyber768" );

// Sender encapsulates using recipient's public key
encapResult = KyberEncapsulate( keys.public );
// Sender transmits encapResult.ciphertext to the recipient

// Recipient decapsulates to recover the shared secret
sharedSecret = KyberDecapsulate( keys.private, encapResult.ciphertext );

// Use the shared secret for symmetric decryption
recipientKey = binaryEncode( sharedSecret, "base64" );
// decrypted = Decrypt( encrypted, recipientKey, "AES/CBC/PKCS5Padding", "Base64" );

// Wrong private key produces a different (incorrect) shared secret
// rather than throwing an error - this is by design (implicit rejection)

See also