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| 1 | +package pkcs7 |
| 2 | + |
| 3 | +import ( |
| 4 | + "bytes" |
| 5 | + "errors" |
| 6 | +) |
| 7 | + |
| 8 | +var encodeIndent = 0 |
| 9 | + |
| 10 | +type asn1Object interface { |
| 11 | + EncodeTo(writer *bytes.Buffer) error |
| 12 | +} |
| 13 | + |
| 14 | +type asn1Structured struct { |
| 15 | + tagBytes []byte |
| 16 | + content []asn1Object |
| 17 | +} |
| 18 | + |
| 19 | +func (s asn1Structured) EncodeTo(out *bytes.Buffer) error { |
| 20 | + //fmt.Printf("%s--> tag: % X\n", strings.Repeat("| ", encodeIndent), s.tagBytes) |
| 21 | + encodeIndent++ |
| 22 | + inner := new(bytes.Buffer) |
| 23 | + for _, obj := range s.content { |
| 24 | + err := obj.EncodeTo(inner) |
| 25 | + if err != nil { |
| 26 | + return err |
| 27 | + } |
| 28 | + } |
| 29 | + encodeIndent-- |
| 30 | + out.Write(s.tagBytes) |
| 31 | + encodeLength(out, inner.Len()) |
| 32 | + out.Write(inner.Bytes()) |
| 33 | + return nil |
| 34 | +} |
| 35 | + |
| 36 | +type asn1Primitive struct { |
| 37 | + tagBytes []byte |
| 38 | + length int |
| 39 | + content []byte |
| 40 | +} |
| 41 | + |
| 42 | +func (p asn1Primitive) EncodeTo(out *bytes.Buffer) error { |
| 43 | + _, err := out.Write(p.tagBytes) |
| 44 | + if err != nil { |
| 45 | + return err |
| 46 | + } |
| 47 | + if err = encodeLength(out, p.length); err != nil { |
| 48 | + return err |
| 49 | + } |
| 50 | + //fmt.Printf("%s--> tag: % X length: %d\n", strings.Repeat("| ", encodeIndent), p.tagBytes, p.length) |
| 51 | + //fmt.Printf("%s--> content length: %d\n", strings.Repeat("| ", encodeIndent), len(p.content)) |
| 52 | + out.Write(p.content) |
| 53 | + |
| 54 | + return nil |
| 55 | +} |
| 56 | + |
| 57 | +func ber2der(ber []byte) ([]byte, error) { |
| 58 | + if len(ber) == 0 { |
| 59 | + return nil, errors.New("ber2der: input ber is empty") |
| 60 | + } |
| 61 | + //fmt.Printf("--> ber2der: Transcoding %d bytes\n", len(ber)) |
| 62 | + out := new(bytes.Buffer) |
| 63 | + |
| 64 | + obj, _, err := readObject(ber, 0) |
| 65 | + if err != nil { |
| 66 | + return nil, err |
| 67 | + } |
| 68 | + obj.EncodeTo(out) |
| 69 | + |
| 70 | + // if offset < len(ber) { |
| 71 | + // return nil, fmt.Errorf("ber2der: Content longer than expected. Got %d, expected %d", offset, len(ber)) |
| 72 | + //} |
| 73 | + |
| 74 | + return out.Bytes(), nil |
| 75 | +} |
| 76 | + |
| 77 | +// encodes lengths that are longer than 127 into string of bytes |
| 78 | +func marshalLongLength(out *bytes.Buffer, i int) (err error) { |
| 79 | + n := lengthLength(i) |
| 80 | + |
| 81 | + for ; n > 0; n-- { |
| 82 | + err = out.WriteByte(byte(i >> uint((n-1)*8))) |
| 83 | + if err != nil { |
| 84 | + return |
| 85 | + } |
| 86 | + } |
| 87 | + |
| 88 | + return nil |
| 89 | +} |
| 90 | + |
| 91 | +// computes the byte length of an encoded length value |
| 92 | +func lengthLength(i int) (numBytes int) { |
| 93 | + numBytes = 1 |
| 94 | + for i > 255 { |
| 95 | + numBytes++ |
| 96 | + i >>= 8 |
| 97 | + } |
| 98 | + return |
| 99 | +} |
| 100 | + |
| 101 | +// encodes the length in DER format |
| 102 | +// If the length fits in 7 bits, the value is encoded directly. |
| 103 | +// |
| 104 | +// Otherwise, the number of bytes to encode the length is first determined. |
| 105 | +// This number is likely to be 4 or less for a 32bit length. This number is |
| 106 | +// added to 0x80. The length is encoded in big endian encoding follow after |
| 107 | +// |
| 108 | +// Examples: |
| 109 | +// length | byte 1 | bytes n |
| 110 | +// 0 | 0x00 | - |
| 111 | +// 120 | 0x78 | - |
| 112 | +// 200 | 0x81 | 0xC8 |
| 113 | +// 500 | 0x82 | 0x01 0xF4 |
| 114 | +// |
| 115 | +func encodeLength(out *bytes.Buffer, length int) (err error) { |
| 116 | + if length >= 128 { |
| 117 | + l := lengthLength(length) |
| 118 | + err = out.WriteByte(0x80 | byte(l)) |
| 119 | + if err != nil { |
| 120 | + return |
| 121 | + } |
| 122 | + err = marshalLongLength(out, length) |
| 123 | + if err != nil { |
| 124 | + return |
| 125 | + } |
| 126 | + } else { |
| 127 | + err = out.WriteByte(byte(length)) |
| 128 | + if err != nil { |
| 129 | + return |
| 130 | + } |
| 131 | + } |
| 132 | + return |
| 133 | +} |
| 134 | + |
| 135 | +func readObject(ber []byte, offset int) (asn1Object, int, error) { |
| 136 | + berLen := len(ber) |
| 137 | + if offset >= berLen { |
| 138 | + return nil, 0, errors.New("ber2der: offset is after end of ber data") |
| 139 | + } |
| 140 | + tagStart := offset |
| 141 | + b := ber[offset] |
| 142 | + offset++ |
| 143 | + if offset >= berLen { |
| 144 | + return nil, 0, errors.New("ber2der: cannot move offset forward, end of ber data reached") |
| 145 | + } |
| 146 | + tag := b & 0x1F // last 5 bits |
| 147 | + if tag == 0x1F { |
| 148 | + tag = 0 |
| 149 | + for ber[offset] >= 0x80 { |
| 150 | + tag = tag*128 + ber[offset] - 0x80 |
| 151 | + offset++ |
| 152 | + if offset > berLen { |
| 153 | + return nil, 0, errors.New("ber2der: cannot move offset forward, end of ber data reached") |
| 154 | + } |
| 155 | + } |
| 156 | + // jvehent 20170227: this doesn't appear to be used anywhere... |
| 157 | + //tag = tag*128 + ber[offset] - 0x80 |
| 158 | + offset++ |
| 159 | + if offset > berLen { |
| 160 | + return nil, 0, errors.New("ber2der: cannot move offset forward, end of ber data reached") |
| 161 | + } |
| 162 | + } |
| 163 | + tagEnd := offset |
| 164 | + |
| 165 | + kind := b & 0x20 |
| 166 | + if kind == 0 { |
| 167 | + debugprint("--> Primitive\n") |
| 168 | + } else { |
| 169 | + debugprint("--> Constructed\n") |
| 170 | + } |
| 171 | + // read length |
| 172 | + var length int |
| 173 | + l := ber[offset] |
| 174 | + offset++ |
| 175 | + if offset > berLen { |
| 176 | + return nil, 0, errors.New("ber2der: cannot move offset forward, end of ber data reached") |
| 177 | + } |
| 178 | + hack := 0 |
| 179 | + if l > 0x80 { |
| 180 | + numberOfBytes := (int)(l & 0x7F) |
| 181 | + if numberOfBytes > 4 { // int is only guaranteed to be 32bit |
| 182 | + return nil, 0, errors.New("ber2der: BER tag length too long") |
| 183 | + } |
| 184 | + if numberOfBytes == 4 && (int)(ber[offset]) > 0x7F { |
| 185 | + return nil, 0, errors.New("ber2der: BER tag length is negative") |
| 186 | + } |
| 187 | + if (int)(ber[offset]) == 0x0 { |
| 188 | + return nil, 0, errors.New("ber2der: BER tag length has leading zero") |
| 189 | + } |
| 190 | + debugprint("--> (compute length) indicator byte: %x\n", l) |
| 191 | + debugprint("--> (compute length) length bytes: % X\n", ber[offset:offset+numberOfBytes]) |
| 192 | + for i := 0; i < numberOfBytes; i++ { |
| 193 | + length = length*256 + (int)(ber[offset]) |
| 194 | + offset++ |
| 195 | + if offset > berLen { |
| 196 | + return nil, 0, errors.New("ber2der: cannot move offset forward, end of ber data reached") |
| 197 | + } |
| 198 | + } |
| 199 | + } else if l == 0x80 { |
| 200 | + // find length by searching content |
| 201 | + markerIndex := bytes.LastIndex(ber[offset:], []byte{0x0, 0x0}) |
| 202 | + if markerIndex == -1 { |
| 203 | + return nil, 0, errors.New("ber2der: Invalid BER format") |
| 204 | + } |
| 205 | + length = markerIndex |
| 206 | + hack = 2 |
| 207 | + debugprint("--> (compute length) marker found at offset: %d\n", markerIndex+offset) |
| 208 | + } else { |
| 209 | + length = (int)(l) |
| 210 | + } |
| 211 | + if length < 0 { |
| 212 | + return nil, 0, errors.New("ber2der: invalid negative value found in BER tag length") |
| 213 | + } |
| 214 | + //fmt.Printf("--> length : %d\n", length) |
| 215 | + contentEnd := offset + length |
| 216 | + if contentEnd > len(ber) { |
| 217 | + return nil, 0, errors.New("ber2der: BER tag length is more than available data") |
| 218 | + } |
| 219 | + debugprint("--> content start : %d\n", offset) |
| 220 | + debugprint("--> content end : %d\n", contentEnd) |
| 221 | + debugprint("--> content : % X\n", ber[offset:contentEnd]) |
| 222 | + var obj asn1Object |
| 223 | + if kind == 0 { |
| 224 | + obj = asn1Primitive{ |
| 225 | + tagBytes: ber[tagStart:tagEnd], |
| 226 | + length: length, |
| 227 | + content: ber[offset:contentEnd], |
| 228 | + } |
| 229 | + } else { |
| 230 | + var subObjects []asn1Object |
| 231 | + for offset < contentEnd { |
| 232 | + var subObj asn1Object |
| 233 | + var err error |
| 234 | + subObj, offset, err = readObject(ber[:contentEnd], offset) |
| 235 | + if err != nil { |
| 236 | + return nil, 0, err |
| 237 | + } |
| 238 | + subObjects = append(subObjects, subObj) |
| 239 | + } |
| 240 | + obj = asn1Structured{ |
| 241 | + tagBytes: ber[tagStart:tagEnd], |
| 242 | + content: subObjects, |
| 243 | + } |
| 244 | + } |
| 245 | + |
| 246 | + return obj, contentEnd + hack, nil |
| 247 | +} |
| 248 | + |
| 249 | +func debugprint(format string, a ...interface{}) { |
| 250 | + //fmt.Printf(format, a) |
| 251 | +} |
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