Module: SJCL::Mode::CCM

Defined in:
lib/sjcl/ccm.rb

Defined Under Namespace

Classes: Error, TagAuthError

Constant Summary collapse

NAME = 
"ccm"

Class Method Summary collapse

Class Method Details

.computeTag(prf, plaintext, iv, adata, tlen, l) ⇒ Object 



57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
 
# File 'lib/sjcl/ccm.rb', line 57

def self.computeTag(prf, plaintext, iv, adata, tlen, l)
  tlen /= 8
  if (tlen % 2 != 0 || tlen < 4 || tlen > 16)
    raise Error, "ccm: invalid tag length"
  end

  # mac the flags
  mac = [SJCL::BitArray.partial(8, (adata.length > 0 ? 1<<6 : 0) | ((tlen-2) << 2) | l-1)]

  # mac the iv and length
  mac = SJCL::BitArray.concat(mac, iv)
  mac[3] = (mac[3] || 0) | SJCL::BitArray.bitLength(plaintext)/8
  mac = prf.encrypt(mac)
  i=0

  if (adata.length > 0)
    # mac the associated data.  start with its length...
    tmp = SJCL::BitArray.bitLength(adata)/8;
    if (tmp <= 0xFEFF)
      macData = [SJCL::BitArray.partial(16, tmp)];
    elsif (tmp <= 0xFFFFFFFF)
      macData = SJCL::BitArray.concat([SJCL::BitArray.partial(16,0xFFFE)], [tmp]);
    end

    # mac the data itself
    macData = SJCL::BitArray.concat(macData, adata);
    while i < macData.length
      mac = prf.encrypt(SJCL::BitArray.xor4(mac, macData.slice(i,i+4).concat([0,0,0])));
      i+=4
    end
  end

  i = 0
  while i < plaintext.length
    mac = prf.encrypt(SJCL::BitArray.xor4(mac, plaintext.slice(i,i+4).concat([0,0,0])));
    i+=4
  end

  SJCL::BitArray.clamp(mac, tlen * 8)
end

.ctrMode(prf, data, iv, tag, tlen, ccml) ⇒ Object 



98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
 
# File 'lib/sjcl/ccm.rb', line 98

def self.ctrMode(prf, data, iv, tag, tlen, ccml)
  l = data.length
  data = data.dup
  bl= SJCL::BitArray.bitLength(data)
  ctr = SJCL::BitArray.concat([SJCL::BitArray.partial(8,ccml-1)],iv).concat([0,0,0]).slice(0,4)
  tag = SJCL::BitArray.xor4(tag,prf.encrypt(ctr))
  tag = SJCL::BitArray.bitSlice(tag, 0, tlen)
  return {tag:tag, data:[]} if (l == 0)
  i = 0
  while i < l
    ctr[3] += 1;
    enc = prf.encrypt(ctr);
    data[i]   = (data[i] || 0) ^ enc[0];
    data[i+1]   = (data[i+1] || 0) ^ enc[1];
    data[i+2]   = (data[i+2] || 0) ^ enc[2];
    data[i+3]   = (data[i+3] || 0) ^ enc[3];
    i += 4
  end
  return { tag: tag, data: SJCL::BitArray.clamp(data,bl) }
end

.decrypt(prf, ciphertext, iv, adata = [], tlen = 64) ⇒ Object

Raises:



26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
 
# File 'lib/sjcl/ccm.rb', line 26

def self.decrypt(prf, ciphertext, iv, adata=[], tlen=64)
  ccml = 2
  ivl = SJCL::BitArray.bitLength(iv) / 8
  ol = SJCL::BitArray.bitLength(ciphertext)
  out = SJCL::BitArray.clamp(ciphertext, ol - tlen)
  tag = SJCL::BitArray.bitSlice(ciphertext, ol - tlen)

  ol = (ol - tlen) / 8;
  raise Error, "ccm: iv must be at least 7 bytes" if (ivl < 7)

  # compute the length of the length
  while ccml < 4 && ((ol & 0xFFFFFFFF) >> 8*ccml > 0)
    ccml += 1
  end

  if (ccml < 15 - ivl)
    ccml = 15-ivl
  end
  iv = SJCL::BitArray.clamp(iv,8*(15-ccml))

  # decrypt
  out = ctrMode(prf, out, iv, tag, tlen, ccml)

  # check the tag
  tag2 = computeTag(prf, out[:data], iv, adata, tlen, ccml)
  if (!SJCL::BitArray.compare(out[:tag], tag2))
    raise TagAuthError, "ccm: tag doesn't match"
  end
  return out[:data]
end

.encrypt(prf, plaintext, iv, adata = [], tlen = 64) ⇒ Object

Raises:



8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
 
# File 'lib/sjcl/ccm.rb', line 8

def self.encrypt(prf, plaintext, iv, adata=[], tlen=64)
  ccml = 2
  out = plaintext.dup
  ivl = SJCL::BitArray.bitLength(iv) / 8
  ol = SJCL::BitArray.bitLength(out) / 8
  raise Error, "ccm: IV must be at least 7 bytes" if ivl < 7
  while ccml < 4 && ((ol & 0xFFFFFFFF) >> 8*ccml > 0)
    ccml += 1
  end
  ccml = 15 - ivl if ccml < 15 - ivl
  iv = SJCL::BitArray.clamp(iv,8*(15-ccml));
  tag = computeTag(prf, plaintext, iv, adata, tlen, ccml)

  # encrypt
  out = ctrMode(prf, out, iv, tag, tlen, ccml)
  SJCL::BitArray.concat(out[:data], out[:tag])
end