SDK utilities

The zeroecho.sdk.util package provides small, focused utilities for key derivation and password generation. Both classes are stateless and thread-safe.

Kdf — key derivation

Kdf exposes a single static method for HKDF-SHA256 key derivation, suitable for expanding a shared secret (such as the output of an AgreementContext or HybridKexContext) into keying material of any required length.

Kdf.hkdfSha256(byte[] ikm, byte[] salt, byte[] info, int length)
    throws GeneralSecurityException

Parameter	Meaning
ikm	Input keying material (e.g. a raw DH shared secret).
salt	Optional HMAC salt; null uses the RFC 5869 zero-filled default (length of the hash output).
info	Optional application-specific context label (null is accepted).
length	Output length in bytes; must be positive and at most 255 × hash-output-length (8 160 bytes for SHA-256).

The call throws GeneralSecurityException if the required JCA algorithm is unavailable or length is out of range.

Example

import zeroecho.sdk.util.Kdf;
import zeroecho.core.alg.xdh.XdhSpec;
import zeroecho.core.context.AgreementContext;

// "Xdh" is the ZeroEcho registry id for XDH; XdhSpec.X25519 selects the X25519 curve.
AgreementContext agreement = session.createContext("Xdh",
        zeroecho.core.KeyUsage.AGREEMENT, myPrivateKey, XdhSpec.X25519);
agreement.setPeerPublic(peerPublicKey);
byte[] rawSecret = agreement.deriveSecret();

byte[] keyMaterial = Kdf.hkdfSha256(
        rawSecret,
        null,                                          // default salt
        "MyProtocol/v1/session-key".getBytes(),        // domain separator
        32);                                           // 256-bit output

Zero the rawSecret array promptly after calling hkdfSha256.

Password — random password generation

Password generates random passwords suitable for use as keyring passwords or one-time credentials. It does not handle storage or verification.

Method	Description
generateRandom(byte[] dest)	Fills dest with cryptographically random bytes.
generatePrintablePasswordChars(int length)	Returns a char[] of length printable ASCII characters (printable range 33–126).

import zeroecho.sdk.util.Password;
import zeroecho.core.storage.KeyringPassword;
import java.util.Arrays;

// Generate a 32-character printable password and hand it to a KeyringPassword.
char[] raw = Password.generatePrintablePasswordChars(32);
try (KeyringPassword password = new KeyringPassword(raw)) {
    Arrays.fill(raw, '\0');         // caller clears its copy; KeyringPassword owns its own
    // use password …
}
// password.destroy() is called automatically by try-with-resources

Both methods use a SecureRandom source. Always zero the returned char[] after handing it to the consumer; KeyringPassword makes its own defensive copy and clears it when destroyed.