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(kdf_id) ⇒ DHKEM

Returns a new instance of DHKEM.

Raises:

  • (Exception) 


9
10
11
12
13
14
 
# File 'lib/hpke/dhkem.rb', line 9

def initialize(kdf_id)
  # Currently all KDFs are HKDF so this works fine,
  # but when other KDFs are added, this should be fixed
  @hkdf = HPKE::HKDF.new(kdf_id)
  raise Exception.new('KDF not compatible with DHKEM curve') unless @hkdf.n_h == self.n_secret
end

Instance Method Details

#auth_decap(enc, sk_r, pk_s) ⇒ Object 



58
59
60
61
62
63
64
65
66
67
68
 
# File 'lib/hpke/dhkem.rb', line 58

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 



31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
 
# File 'lib/hpke/dhkem.rb', line 31

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 



85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
 
# File 'lib/hpke/dhkem.rb', line 85

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 



47
48
49
50
51
52
53
54
55
56
 
# File 'lib/hpke/dhkem.rb', line 47

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) —-



106
107
108
109
110
111
 
# File 'lib/hpke/dhkem.rb', line 106

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 



117
118
119
120
121
122
123
124
125
126
 
# File 'lib/hpke/dhkem.rb', line 117

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 



16
17
18
19
20
21
22
23
24
25
26
27
28
29
 
# File 'lib/hpke/dhkem.rb', line 16

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 



70
71
72
73
74
75
76
77
78
79
80
81
82
83
 
# File 'lib/hpke/dhkem.rb', line 70

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 



101
102
103
 
# File 'lib/hpke/dhkem.rb', line 101

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

#serialize_public_key(pk) ⇒ Object 



113
114
115
 
# File 'lib/hpke/dhkem.rb', line 113

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