Class: HPKE::DHKEM

Inherits:
Object
  • Object
show all
Includes:
Util
Defined in:
lib/hpke/dhkem.rb

Direct Known Subclasses

EC, X25519, X448

Defined Under Namespace

Classes: EC, X25519, X448

Instance Method Summary collapse

Methods included from Util

#i2osp, #os2ip, #xor

Constructor Details

#initialize(hash_name) ⇒ DHKEM

Returns a new instance of DHKEM.



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# File 'lib/hpke/dhkem.rb', line 9

def initialize(hash_name)
  @hkdf = HPKE::HKDF.new(hash_name)
end

Instance Method Details

#auth_decap(enc, sk_r, pk_s) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 55

def auth_decap(enc, sk_r, pk_s)
  pk_e = deserialize_public_key(enc)
  dh = sk_r.derive(pk_e) + sk_r.derive(pk_s)

  pkrm = serialize_public_key(sk_r)
  pksm = serialize_public_key(pk_s)
  kem_context = enc + pkrm + pksm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  shared_secret
end

#auth_encap(pk_r, sk_s) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 28

def auth_encap(pk_r, sk_s)
  pkey_e = generate_key_pair()
  dh = pkey_e.derive(pk_r) + sk_s.derive(pk_r)
  enc = serialize_public_key(pkey_e)

  pkrm = serialize_public_key(pk_r)
  pksm = serialize_public_key(sk_s)
  kem_context = enc + pkrm + pksm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  {
    shared_secret: shared_secret,
    enc: enc
  }
end

#auth_encap_fixed(pk_r, sk_s, ikm_e) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 82

def auth_encap_fixed(pk_r, sk_s, ikm_e)
  pkey_e = derive_key_pair(ikm_e)
  dh = pkey_e.derive(pk_r) + sk_s.derive(pk_r)
  enc = serialize_public_key(pkey_e)

  pkrm = serialize_public_key(pk_r)
  pksm = serialize_public_key(sk_s)
  kem_context = enc + pkrm + pksm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  {
    shared_secret: shared_secret,
    enc: enc
  }
end

#decap(enc, sk_r) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 44

def decap(enc, sk_r)
  pk_e = deserialize_public_key(enc)
  dh = sk_r.derive(pk_e)

  pkrm = serialize_public_key(sk_r)
  kem_context = enc + pkrm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  shared_secret
end

#derive_key_pair(ikm) ⇒ Object

—- functions for Edwards curves (X25519, X448) —-



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# File 'lib/hpke/dhkem.rb', line 103

def derive_key_pair(ikm)
  dkp_prk = @hkdf.labeled_extract('', 'dkp_prk', ikm, kem_suite_id)
  sk = @hkdf.labeled_expand(dkp_prk, 'sk', '', n_sk, kem_suite_id)

  create_key_pair_from_secret(sk)
end

#deserialize_public_key(serialized_pk) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 114

def deserialize_public_key(serialized_pk)
  asn1_seq_pub = OpenSSL::ASN1.Sequence([
    OpenSSL::ASN1.Sequence([
      OpenSSL::ASN1.ObjectId(asn1_oid)
    ]),
    OpenSSL::ASN1.BitString(serialized_pk)
  ])

  OpenSSL::PKey.read(asn1_seq_pub.to_der)
end

#encap(pk_r) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 13

def encap(pk_r)
  pkey_e = generate_key_pair()
  dh = pkey_e.derive(pk_r)
  enc = serialize_public_key(pkey_e)

  pkrm = serialize_public_key(pk_r)
  kem_context = enc + pkrm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  {
    shared_secret: shared_secret,
    enc: enc
  }
end

#encap_fixed(pk_r, ikm_e) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 67

def encap_fixed(pk_r, ikm_e)
  pkey_e = derive_key_pair(ikm_e)
  dh = pkey_e.derive(pk_r)
  enc = serialize_public_key(pkey_e)

  pkrm = serialize_public_key(pk_r)
  kem_context = enc + pkrm

  shared_secret = extract_and_expand(dh, kem_context, kem_suite_id)
  {
    shared_secret: shared_secret,
    enc: enc
  }
end

#generate_key_pair ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 98

def generate_key_pair
  derive_key_pair(SecureRandom.random_bytes(n_sk))
end

#serialize_public_key(pk) ⇒ Object 



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# File 'lib/hpke/dhkem.rb', line 110

def serialize_public_key(pk)
  pk.public_to_der[-n_pk, n_pk]
end