path: root/crypto/ecies/params.go

package ecies

// This file contains parameters for ECIES encryption, specifying the
// symmetric encryption and HMAC parameters.

import (
    "crypto"
    "crypto/aes"
    "crypto/cipher"
    "crypto/elliptic"
    "crypto/sha256"
    "crypto/sha512"
    "fmt"
    "hash"
)

// The default curve for this package is the NIST P256 curve, which
// provides security equivalent to AES-128.
var DefaultCurve = elliptic.P256()

var (
    ErrUnsupportedECDHAlgorithm   = fmt.Errorf("ecies: unsupported ECDH algorithm")
    ErrUnsupportedECIESParameters = fmt.Errorf("ecies: unsupported ECIES parameters")
)

type ECIESParams struct {
    Hash      func() hash.Hash // hash function
    hashAlgo  crypto.Hash
    Cipher    func([]byte) (cipher.Block, error) // symmetric cipher
    BlockSize int                                // block size of symmetric cipher
    KeyLen    int                                // length of symmetric key
}

// Standard ECIES parameters:
// * ECIES using AES128 and HMAC-SHA-256-16
// * ECIES using AES256 and HMAC-SHA-256-32
// * ECIES using AES256 and HMAC-SHA-384-48
// * ECIES using AES256 and HMAC-SHA-512-64

var (
    ECIES_AES128_SHA256 = &ECIESParams{
        Hash:      sha256.New,
        hashAlgo:  crypto.SHA256,
        Cipher:    aes.NewCipher,
        BlockSize: aes.BlockSize,
        KeyLen:    16,
    }

    ECIES_AES256_SHA256 = &ECIESParams{
        Hash:      sha256.New,
        hashAlgo:  crypto.SHA256,
        Cipher:    aes.NewCipher,
        BlockSize: aes.BlockSize,
        KeyLen:    32,
    }

    ECIES_AES256_SHA384 = &ECIESParams{
        Hash:      sha512.New384,
        hashAlgo:  crypto.SHA384,
        Cipher:    aes.NewCipher,
        BlockSize: aes.BlockSize,
        KeyLen:    32,
    }

    ECIES_AES256_SHA512 = &ECIESParams{
        Hash:      sha512.New,
        hashAlgo:  crypto.SHA512,
        Cipher:    aes.NewCipher,
        BlockSize: aes.BlockSize,
        KeyLen:    32,
    }
)

var paramsFromCurve = map[elliptic.Curve]*ECIESParams{
    elliptic.P256(): ECIES_AES128_SHA256,
    elliptic.P384(): ECIES_AES256_SHA384,
    elliptic.P521(): ECIES_AES256_SHA512,
}

func AddParamsForCurve(curve elliptic.Curve, params *ECIESParams) {
    paramsFromCurve[curve] = params
}

// ParamsFromCurve selects parameters optimal for the selected elliptic curve.
// Only the curves P256, P384, and P512 are supported.
func ParamsFromCurve(curve elliptic.Curve) (params *ECIESParams) {
    return paramsFromCurve[curve]

    /*
        switch curve {
        case elliptic.P256():
            return ECIES_AES128_SHA256
        case elliptic.P384():
            return ECIES_AES256_SHA384
        case elliptic.P521():
            return ECIES_AES256_SHA512
        default:
            return nil
        }
    */
}

// ASN.1 encode the ECIES parameters relevant to the encryption operations.
func paramsToASNECIES(params *ECIESParams) (asnParams asnECIESParameters) {
    if nil == params {
        return
    }
    asnParams.KDF = asnNISTConcatenationKDF
    asnParams.MAC = hmacFull
    switch params.KeyLen {
    case 16:
        asnParams.Sym = aes128CTRinECIES
    case 24:
        asnParams.Sym = aes192CTRinECIES
    case 32:
        asnParams.Sym = aes256CTRinECIES
    }
    return
}

// ASN.1 encode the ECIES parameters relevant to ECDH.
func paramsToASNECDH(params *ECIESParams) (algo asnECDHAlgorithm) {
    switch params.hashAlgo {
    case crypto.SHA224:
        algo = dhSinglePass_stdDH_sha224kdf
    case crypto.SHA256:
        algo = dhSinglePass_stdDH_sha256kdf
    case crypto.SHA384:
        algo = dhSinglePass_stdDH_sha384kdf
    case crypto.SHA512:
        algo = dhSinglePass_stdDH_sha512kdf
    }
    return
}

// ASN.1 decode the ECIES parameters relevant to the encryption stage.
func asnECIEStoParams(asnParams asnECIESParameters, params *ECIESParams) {
    if !asnParams.KDF.Cmp(asnNISTConcatenationKDF) {
        params = nil
        return
    } else if !asnParams.MAC.Cmp(hmacFull) {
        params = nil
        return
    }

    switch {
    case asnParams.Sym.Cmp(aes128CTRinECIES):
        params.KeyLen = 16
        params.BlockSize = 16
        params.Cipher = aes.NewCipher
    case asnParams.Sym.Cmp(aes192CTRinECIES):
        params.KeyLen = 24
        params.BlockSize = 16
        params.Cipher = aes.NewCipher
    case asnParams.Sym.Cmp(aes256CTRinECIES):
        params.KeyLen = 32
        params.BlockSize = 16
        params.Cipher = aes.NewCipher
    default:
        params = nil
    }
}

// ASN.1 decode the ECIES parameters relevant to ECDH.
func asnECDHtoParams(asnParams asnECDHAlgorithm, params *ECIESParams) {
    if asnParams.Cmp(dhSinglePass_stdDH_sha224kdf) {
        params.hashAlgo = crypto.SHA224
        params.Hash = sha256.New224
    } else if asnParams.Cmp(dhSinglePass_stdDH_sha256kdf) {
        params.hashAlgo = crypto.SHA256
        params.Hash = sha256.New
    } else if asnParams.Cmp(dhSinglePass_stdDH_sha384kdf) {
        params.hashAlgo = crypto.SHA384
        params.Hash = sha512.New384
    } else if asnParams.Cmp(dhSinglePass_stdDH_sha512kdf) {
        params.hashAlgo = crypto.SHA512
        params.Hash = sha512.New
    } else {
        params = nil
    }
}