schastsp/src/git.xdrm.io/schastsp/client/keyset/keyset.go

package keyset

import (
	"io"
	"encoding/binary"
	"errors"
	"git.xdrm.io/schastsp/lib/scha"
	"math/rand"
	"time"
)

const a = 12

/* Attributes */
type Set struct {
	min   uint16 // min depth
	depth uint16 // cur depth
	max   uint16 // max depth

	sec         []byte // secret
	consumption uint   // consumption level
	// 0: none
	// 1: need to migrate
	// 2: waiting migration
	// 3: validated migration
}

/* (1) Creates a new KeySet
*
* @min<uint16>						Minimum depth value
* @max<uint16>						Maximum depth value
*
* @return outName<outType>			outDesc
*
---------------------------------------------------------*/
func Create(min uint16, max uint16) (*Set, error) {

	/* (1) Fail if min >= max */
	if min >= max {
		return nil, errors.New("Max depth is not greater than Min depth")
	}

	/* (2) Instanciate */
	var instance = new(Set)

	/* (3) Set attributes */
	instance.min = min
	instance.max = max

	/* (4) Generate values if <nil> secret */
	if instance.sec == nil {
		instance.generate()
	}

	return instance, nil
}

/* (2) Generates a pseudo-random KeySet
*
---------------------------------------------------------*/
func (s *Set) generate() {

	/* (1) Seed randomness */
	rand.Seed(time.Now().UTC().UnixNano())

	/* (1) Generate new secret
	---------------------------------------------------------*/
	/* (1) Reset current secret */
	s.sec = make([]byte, scha.HSIZE)

	/* (2) Generate each char. until same length as hash digest */
	for i := uint16(0); i < scha.HSIZE; i++ {
		s.sec[i] = byte(rand.Int() % 256)
	}

	/* (2) Manage other attributes
	---------------------------------------------------------*/
	/* (1) Random depth pick init */
	var randMin, randMax uint16 = s.min + (s.max-s.min)/2, s.max

	/* (2) Select "random" depth */
	s.depth = randMin + uint16(rand.Intn(int(randMax-randMin)))

	/* (3) Reset comsumption level */
	s.consumption = 0

}

/* (3) Get current hash
*
* @return digest<[]byte]>			Current hash representing the set
*
---------------------------------------------------------*/
func (s Set) Hash() ([]byte, error) {

	/* (1) Get digest */
	digest, err := scha.Hash(s.sec, uint(s.depth), nil, nil)

	/* (2) Dispatch error */
	if err != nil {
		return nil, err
	}

	/* (3) Else -> return digest */
	return digest, nil

}

/* (4) Decrement depth
*
* @return remaining<uint>			Remaining hashes before migration
*
---------------------------------------------------------*/
func (s *Set) Decrement() uint16 {

	/* (1) Decrement the depth */
	s.depth--

	/* (2) If near minDepth (10 far): set consumption to 1 */
	if s.depth <= s.min+10 {
		s.consumption = 1
	}

	/* (3) Return remaining attempts */
	return s.depth - s.max

}

/* (5) Serialisation
*
* @return serial<string>			String representation
*
*
* === FORMAT ===
*
* |   hsize   |   secret   |  depth  |
* +-----------+------------+---------+
* |  16 bits  | hsize bits | 16 bits |
*
* == ENDIANNESS ==
*
* network endianness -> big-endian
*
---------------------------------------------------------*/
func (s *Set) Write(writer io.Writer) error {

	var err error;

	/* (1) Copy hash size */
	err = binary.Write(writer, binary.BigEndian, scha.HSIZE)
	if err != nil { return err }

	/* (2) Copy secret */
	err = binary.Write(writer, binary.BigEndian, s.sec)
	if err != nil { return err }

	/* (3) Copy depth */
	err = binary.Write(writer, binary.BigEndian, s.depth)
	if err != nil { return err }

	return nil

}

/* (6) Builds a KeySet from its serial representation
*
* @serial<string>			String representation
*
* @return instance<*Set>	The corresponding set
* @return err<error>		Optional error
*
* === FORMAT ===
*
* |   hsize   |   secret   |  depth  |
* +-----------+------------+---------+
* |  16 bits  | hsize bits | 16 bits |
*
---------------------------------------------------------*/
func (s *Set) Read(reader io.Reader) error {

	var (
		err error
		secretLength uint16
	)

	/* (1) Read the secret size */
	err = binary.Read(reader, binary.BigEndian, &secretLength)
	if err != nil {
		return err
	}

	/* (2) Fail if secretLength different than digest size */
	if secretLength != scha.HSIZE {
		return errors.New("Invalid secret size (must be the same as digest size)")
	}

	/* (3) Try to copy the secret */
	err = binary.Read(reader, binary.BigEndian, &s.sec)
	if err != nil { return err }

	/* (4) Manage invalid secret size (mismatch secretLength) */
	if uint16(len(s.sec)) != secretLength {
		return errors.New("Mismatching secret size")
	}

	/* (5) Try to copy the depth */
	err = binary.Read(reader, binary.BigEndian, &s.depth)
	if err != nil { return err }

	return nil

}