// Counter returns the TOTP's 8-byte counter as unsigned 64-bit integer.
func (otp *Totp) getIntCounter() uint64 {
return bigendian.FromUint64(otp.counter)
}
// TOTPFromBytes converts a byte array to a totp object
// it stores the state of the TOTP object, like the key, the current counter, the client offset,
// the total amount of verification failures and the last time a verification happened
func TOTPFromBytes(encryptedMessage []byte, issuer string) (*Totp, error) {
// init the cryptoengine
engine, err := cryptoengine.InitCryptoEngine(issuer)
if err != nil {
return nil, err
}
// decrypt the message
data, err := engine.Decrypt(encryptedMessage)
if err != nil {
return nil, err
}
// new reader
reader := bytes.NewReader([]byte(data.Text))
// otp object
otp := new(Totp)
// get the lenght
lenght := make([]byte, 4)
_, err = reader.Read(lenght) // read the 4 bytes for the total lenght
if err != nil && err != io.EOF {
return otp, err
}
totalSize := bigendian.FromInt([4]byte{lenght[0], lenght[1], lenght[2], lenght[3]})
buffer := make([]byte, totalSize-4)
_, err = reader.Read(buffer)
if err != nil && err != io.EOF {
return otp, err
}
// skip the total bytes size
startOffset := 0
// read key size
endOffset := startOffset + 4
keyBytes := buffer[startOffset:endOffset]
keySize := bigendian.FromInt([4]byte{keyBytes[0], keyBytes[1], keyBytes[2], keyBytes[3]})
// read the key
startOffset = endOffset
endOffset = startOffset + keySize
otp.key = buffer[startOffset:endOffset]
// read the counter
startOffset = endOffset
endOffset = startOffset + 8
b := buffer[startOffset:endOffset]
otp.counter = [8]byte{b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7]}
// read the digits
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
otp.digits = bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]}) //
// read the issuer size
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
issuerSize := bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
// read the issuer string
startOffset = endOffset
endOffset = startOffset + issuerSize
otp.issuer = string(buffer[startOffset:endOffset])
// read the account size
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
accountSize := bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
// read the account string
startOffset = endOffset
endOffset = startOffset + accountSize
otp.account = string(buffer[startOffset:endOffset])
// read the steps
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
otp.stepSize = bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
// read the offset
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
otp.clientOffset = bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
// read the total failuers
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
otp.totalVerificationFailures = bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
// read the offset
startOffset = endOffset
endOffset = startOffset + 8
b = buffer[startOffset:endOffset]
ts := bigendian.FromUint64([8]byte{b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7]})
otp.lastVerificationTime = time.Unix(int64(ts), 0)
// read the hash type
startOffset = endOffset
endOffset = startOffset + 4
b = buffer[startOffset:endOffset]
hashType := bigendian.FromInt([4]byte{b[0], b[1], b[2], b[3]})
switch hashType {
case 1:
otp.hashFunction = crypto.SHA256
break
case 2:
otp.hashFunction = crypto.SHA512
break
default:
otp.hashFunction = crypto.SHA1
}
return otp, err
}