def get_bolt8_hkdf(salt, ikm):
    """RFC5869 HKDF instantiated in the specific form
    used in Lightning BOLT 8:
    Extract and expand to 64 bytes using HMAC-SHA256,
    with info field set to a zero length string as per BOLT8
    Return as two 32 byte fields.
    """
    #Extract
    prk = hmac_oneshot(salt, msg=ikm, digest=hashlib.sha256)
    assert len(prk) == 32
    #Expand
    info = b""
    T0 = b""
    T1 = hmac_oneshot(prk, T0 + info + b"\x01", digest=hashlib.sha256)
    T2 = hmac_oneshot(prk, T1 + info + b"\x02", digest=hashlib.sha256)
    assert len(T1 + T2) == 64
    return T1, T2
RFC5869 HKDF instantiated in the specific form
    used in Lightning BOLT 8:
    Extract and expand to 64 bytes using HMAC-SHA256,
    with info field set to a zero length string as per BOLT8
    Return as two 32 byte fields.
    
electrum/lntransport.py