kevacoin/src/key.cpp

// Copyright (c) 2009-2013 The Bitcoin developers
// Distributed under the MIT/X11 software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "key.h"

#include <openssl/bn.h>
#include <openssl/ecdsa.h>
#include <openssl/obj_mac.h>
#include <openssl/rand.h>

// anonymous namespace with local implementation code (OpenSSL interaction)
namespace {

// Generate a private key from just the secret parameter
int EC_KEY_regenerate_key(EC_KEY *eckey, BIGNUM *priv_key)
{
    int ok = 0;
    BN_CTX *ctx = NULL;
    EC_POINT *pub_key = NULL;

    if (!eckey) return 0;

    const EC_GROUP *group = EC_KEY_get0_group(eckey);

    if ((ctx = BN_CTX_new()) == NULL)
        goto err;

    pub_key = EC_POINT_new(group);

    if (pub_key == NULL)
        goto err;

    if (!EC_POINT_mul(group, pub_key, priv_key, NULL, NULL, ctx))
        goto err;

    EC_KEY_set_private_key(eckey,priv_key);
    EC_KEY_set_public_key(eckey,pub_key);

    ok = 1;

err:

    if (pub_key)
        EC_POINT_free(pub_key);
    if (ctx != NULL)
        BN_CTX_free(ctx);

    return(ok);
}

// Perform ECDSA key recovery (see SEC1 4.1.6) for curves over (mod p)-fields
// recid selects which key is recovered
// if check is non-zero, additional checks are performed
int ECDSA_SIG_recover_key_GFp(EC_KEY *eckey, ECDSA_SIG *ecsig, const unsigned char *msg, int msglen, int recid, int check)
{
    if (!eckey) return 0;

    int ret = 0;
    BN_CTX *ctx = NULL;

    BIGNUM *x = NULL;
    BIGNUM *e = NULL;
    BIGNUM *order = NULL;
    BIGNUM *sor = NULL;
    BIGNUM *eor = NULL;
    BIGNUM *field = NULL;
    EC_POINT *R = NULL;
    EC_POINT *O = NULL;
    EC_POINT *Q = NULL;
    BIGNUM *rr = NULL;
    BIGNUM *zero = NULL;
    int n = 0;
    int i = recid / 2;

    const EC_GROUP *group = EC_KEY_get0_group(eckey);
    if ((ctx = BN_CTX_new()) == NULL) { ret = -1; goto err; }
    BN_CTX_start(ctx);
    order = BN_CTX_get(ctx);
    if (!EC_GROUP_get_order(group, order, ctx)) { ret = -2; goto err; }
    x = BN_CTX_get(ctx);
    if (!BN_copy(x, order)) { ret=-1; goto err; }
    if (!BN_mul_word(x, i)) { ret=-1; goto err; }
    if (!BN_add(x, x, ecsig->r)) { ret=-1; goto err; }
    field = BN_CTX_get(ctx);
    if (!EC_GROUP_get_curve_GFp(group, field, NULL, NULL, ctx)) { ret=-2; goto err; }
    if (BN_cmp(x, field) >= 0) { ret=0; goto err; }
    if ((R = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
    if (!EC_POINT_set_compressed_coordinates_GFp(group, R, x, recid % 2, ctx)) { ret=0; goto err; }
    if (check)
    {
        if ((O = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
        if (!EC_POINT_mul(group, O, NULL, R, order, ctx)) { ret=-2; goto err; }
        if (!EC_POINT_is_at_infinity(group, O)) { ret = 0; goto err; }
    }
    if ((Q = EC_POINT_new(group)) == NULL) { ret = -2; goto err; }
    n = EC_GROUP_get_degree(group);
    e = BN_CTX_get(ctx);
    if (!BN_bin2bn(msg, msglen, e)) { ret=-1; goto err; }
    if (8*msglen > n) BN_rshift(e, e, 8-(n & 7));
    zero = BN_CTX_get(ctx);
    if (!BN_zero(zero)) { ret=-1; goto err; }
    if (!BN_mod_sub(e, zero, e, order, ctx)) { ret=-1; goto err; }
    rr = BN_CTX_get(ctx);
    if (!BN_mod_inverse(rr, ecsig->r, order, ctx)) { ret=-1; goto err; }
    sor = BN_CTX_get(ctx);
    if (!BN_mod_mul(sor, ecsig->s, rr, order, ctx)) { ret=-1; goto err; }
    eor = BN_CTX_get(ctx);
    if (!BN_mod_mul(eor, e, rr, order, ctx)) { ret=-1; goto err; }
    if (!EC_POINT_mul(group, Q, eor, R, sor, ctx)) { ret=-2; goto err; }
    if (!EC_KEY_set_public_key(eckey, Q)) { ret=-2; goto err; }

    ret = 1;

err:
    if (ctx) {
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
    }
    if (R != NULL) EC_POINT_free(R);
    if (O != NULL) EC_POINT_free(O);
    if (Q != NULL) EC_POINT_free(Q);
    return ret;
}

// RAII Wrapper around OpenSSL's EC_KEY
class CECKey {
private:
    EC_KEY *pkey;

public:
    CECKey() {
        pkey = EC_KEY_new_by_curve_name(NID_secp256k1);
        assert(pkey != NULL);
    }

    ~CECKey() {
        EC_KEY_free(pkey);
    }

    void GetSecretBytes(unsigned char vch[32]) const {
        const BIGNUM *bn = EC_KEY_get0_private_key(pkey);
        assert(bn);
        int nBytes = BN_num_bytes(bn);
        int n=BN_bn2bin(bn,&vch[32 - nBytes]);
        assert(n == nBytes);
        memset(vch, 0, 32 - nBytes);
    }

    void SetSecretBytes(const unsigned char vch[32]) {
        bool ret;
        BIGNUM bn;
        BN_init(&bn);
        ret = BN_bin2bn(vch, 32, &bn);
        assert(ret);
        ret = EC_KEY_regenerate_key(pkey, &bn);
        assert(ret);
        BN_clear_free(&bn);
    }

    void GetPrivKey(CPrivKey &privkey, bool fCompressed) {
        EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
        int nSize = i2d_ECPrivateKey(pkey, NULL);
        assert(nSize);
        privkey.resize(nSize);
        unsigned char* pbegin = &privkey[0];
        int nSize2 = i2d_ECPrivateKey(pkey, &pbegin);
        assert(nSize == nSize2);
    }

    bool SetPrivKey(const CPrivKey &privkey, bool fSkipCheck=false) {
        const unsigned char* pbegin = &privkey[0];
        if (d2i_ECPrivateKey(&pkey, &pbegin, privkey.size())) {
            if(fSkipCheck)
                return true;
            
            // d2i_ECPrivateKey returns true if parsing succeeds.
            // This doesn't necessarily mean the key is valid.
            if (EC_KEY_check_key(pkey))
                return true;
        }
        return false;
    }

    void GetPubKey(CPubKey &pubkey, bool fCompressed) {
        EC_KEY_set_conv_form(pkey, fCompressed ? POINT_CONVERSION_COMPRESSED : POINT_CONVERSION_UNCOMPRESSED);
        int nSize = i2o_ECPublicKey(pkey, NULL);
        assert(nSize);
        assert(nSize <= 65);
        unsigned char c[65];
        unsigned char *pbegin = c;
        int nSize2 = i2o_ECPublicKey(pkey, &pbegin);
        assert(nSize == nSize2);
        pubkey.Set(&c[0], &c[nSize]);
    }

    bool SetPubKey(const CPubKey &pubkey) {
        const unsigned char* pbegin = pubkey.begin();
        return o2i_ECPublicKey(&pkey, &pbegin, pubkey.size());
    }

    bool Sign(const uint256 &hash, std::vector<unsigned char>& vchSig) {
        vchSig.clear();
        ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
        if (sig == NULL)
            return false;
        BN_CTX *ctx = BN_CTX_new();
        BN_CTX_start(ctx);
        const EC_GROUP *group = EC_KEY_get0_group(pkey);
        BIGNUM *order = BN_CTX_get(ctx);
        BIGNUM *halforder = BN_CTX_get(ctx);
        EC_GROUP_get_order(group, order, ctx);
        BN_rshift1(halforder, order);
        if (BN_cmp(sig->s, halforder) > 0) {
            // enforce low S values, by negating the value (modulo the order) if above order/2.
            BN_sub(sig->s, order, sig->s);
        }
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        unsigned int nSize = ECDSA_size(pkey);
        vchSig.resize(nSize); // Make sure it is big enough
        unsigned char *pos = &vchSig[0];
        nSize = i2d_ECDSA_SIG(sig, &pos);
        ECDSA_SIG_free(sig);
        vchSig.resize(nSize); // Shrink to fit actual size
        return true;
    }

    bool Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
        // -1 = error, 0 = bad sig, 1 = good
        if (ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), &vchSig[0], vchSig.size(), pkey) != 1)
            return false;
        return true;
    }

    bool SignCompact(const uint256 &hash, unsigned char *p64, int &rec) {
        bool fOk = false;
        ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
        if (sig==NULL)
            return false;
        memset(p64, 0, 64);
        int nBitsR = BN_num_bits(sig->r);
        int nBitsS = BN_num_bits(sig->s);
        if (nBitsR <= 256 && nBitsS <= 256) {
            CPubKey pubkey;
            GetPubKey(pubkey, true);
            for (int i=0; i<4; i++) {
                CECKey keyRec;
                if (ECDSA_SIG_recover_key_GFp(keyRec.pkey, sig, (unsigned char*)&hash, sizeof(hash), i, 1) == 1) {
                    CPubKey pubkeyRec;
                    keyRec.GetPubKey(pubkeyRec, true);
                    if (pubkeyRec == pubkey) {
                        rec = i;
                        fOk = true;
                        break;
                    }
                }
            }
            assert(fOk);
            BN_bn2bin(sig->r,&p64[32-(nBitsR+7)/8]);
            BN_bn2bin(sig->s,&p64[64-(nBitsS+7)/8]);
        }
        ECDSA_SIG_free(sig);
        return fOk;
    }

    // reconstruct public key from a compact signature
    // This is only slightly more CPU intensive than just verifying it.
    // If this function succeeds, the recovered public key is guaranteed to be valid
    // (the signature is a valid signature of the given data for that key)
    bool Recover(const uint256 &hash, const unsigned char *p64, int rec)
    {
        if (rec<0 || rec>=3)
            return false;
        ECDSA_SIG *sig = ECDSA_SIG_new();
        BN_bin2bn(&p64[0],  32, sig->r);
        BN_bin2bn(&p64[32], 32, sig->s);
        bool ret = ECDSA_SIG_recover_key_GFp(pkey, sig, (unsigned char*)&hash, sizeof(hash), rec, 0) == 1;
        ECDSA_SIG_free(sig);
        return ret;
    }

    static bool TweakSecret(unsigned char vchSecretOut[32], const unsigned char vchSecretIn[32], const unsigned char vchTweak[32])
    {
        bool ret = true;
        BN_CTX *ctx = BN_CTX_new();
        BN_CTX_start(ctx);
        BIGNUM *bnSecret = BN_CTX_get(ctx);
        BIGNUM *bnTweak = BN_CTX_get(ctx);
        BIGNUM *bnOrder = BN_CTX_get(ctx);
        EC_GROUP *group = EC_GROUP_new_by_curve_name(NID_secp256k1);
        EC_GROUP_get_order(group, bnOrder, ctx); // what a grossly inefficient way to get the (constant) group order...
        BN_bin2bn(vchTweak, 32, bnTweak);
        if (BN_cmp(bnTweak, bnOrder) >= 0)
            ret = false; // extremely unlikely
        BN_bin2bn(vchSecretIn, 32, bnSecret);
        BN_add(bnSecret, bnSecret, bnTweak);
        BN_nnmod(bnSecret, bnSecret, bnOrder, ctx);
        if (BN_is_zero(bnSecret))
            ret = false; // ridiculously unlikely
        int nBits = BN_num_bits(bnSecret);
        memset(vchSecretOut, 0, 32);
        BN_bn2bin(bnSecret, &vchSecretOut[32-(nBits+7)/8]);
        EC_GROUP_free(group);
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        return ret;
    }

    bool TweakPublic(const unsigned char vchTweak[32]) {
        bool ret = true;
        BN_CTX *ctx = BN_CTX_new();
        BN_CTX_start(ctx);
        BIGNUM *bnTweak = BN_CTX_get(ctx);
        BIGNUM *bnOrder = BN_CTX_get(ctx);
        BIGNUM *bnOne = BN_CTX_get(ctx);
        const EC_GROUP *group = EC_KEY_get0_group(pkey);
        EC_GROUP_get_order(group, bnOrder, ctx); // what a grossly inefficient way to get the (constant) group order...
        BN_bin2bn(vchTweak, 32, bnTweak);
        if (BN_cmp(bnTweak, bnOrder) >= 0)
            ret = false; // extremely unlikely
        EC_POINT *point = EC_POINT_dup(EC_KEY_get0_public_key(pkey), group);
        BN_one(bnOne);
        EC_POINT_mul(group, point, bnTweak, point, bnOne, ctx);
        if (EC_POINT_is_at_infinity(group, point))
            ret = false; // ridiculously unlikely
        EC_KEY_set_public_key(pkey, point);
        EC_POINT_free(point);
        BN_CTX_end(ctx);
        BN_CTX_free(ctx);
        return ret;
    }
};

int CompareBigEndian(const unsigned char *c1, size_t c1len, const unsigned char *c2, size_t c2len) {
    while (c1len > c2len) {
        if (*c1)
            return 1;
        c1++;
        c1len--;
    }
    while (c2len > c1len) {
        if (*c2)
            return -1;
        c2++;
        c2len--;
    }
    while (c1len > 0) {
        if (*c1 > *c2)
            return 1;
        if (*c2 > *c1)
            return -1;
        c1++;
        c2++;
        c1len--;
    }
    return 0;
}

// Order of secp256k1's generator minus 1.
const unsigned char vchMaxModOrder[32] = {
    0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
    0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFE,
    0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,
    0xBF,0xD2,0x5E,0x8C,0xD0,0x36,0x41,0x40
};

// Half of the order of secp256k1's generator minus 1.
const unsigned char vchMaxModHalfOrder[32] = {
    0x7F,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
    0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
    0x5D,0x57,0x6E,0x73,0x57,0xA4,0x50,0x1D,
    0xDF,0xE9,0x2F,0x46,0x68,0x1B,0x20,0xA0
};

const unsigned char vchZero[0] = {};


}; // end of anonymous namespace

bool CKey::Check(const unsigned char *vch) {
    return CompareBigEndian(vch, 32, vchZero, 0) > 0 &&
           CompareBigEndian(vch, 32, vchMaxModOrder, 32) <= 0;
}

bool CKey::CheckSignatureElement(const unsigned char *vch, int len, bool half) {
    return CompareBigEndian(vch, len, vchZero, 0) > 0 &&
           CompareBigEndian(vch, len, half ? vchMaxModHalfOrder : vchMaxModOrder, 32) <= 0;
}

void CKey::MakeNewKey(bool fCompressedIn) {
    do {
        RAND_bytes(vch, sizeof(vch));
    } while (!Check(vch));
    fValid = true;
    fCompressed = fCompressedIn;
}

bool CKey::SetPrivKey(const CPrivKey &privkey, bool fCompressedIn) {
    CECKey key;
    if (!key.SetPrivKey(privkey))
        return false;
    key.GetSecretBytes(vch);
    fCompressed = fCompressedIn;
    fValid = true;
    return true;
}

CPrivKey CKey::GetPrivKey() const {
    assert(fValid);
    CECKey key;
    key.SetSecretBytes(vch);
    CPrivKey privkey;
    key.GetPrivKey(privkey, fCompressed);
    return privkey;
}

CPubKey CKey::GetPubKey() const {
    assert(fValid);
    CECKey key;
    key.SetSecretBytes(vch);
    CPubKey pubkey;
    key.GetPubKey(pubkey, fCompressed);
    return pubkey;
}

bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
    if (!fValid)
        return false;
    CECKey key;
    key.SetSecretBytes(vch);
    return key.Sign(hash, vchSig);
}

bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
    if (!fValid)
        return false;
    CECKey key;
    key.SetSecretBytes(vch);
    vchSig.resize(65);
    int rec = -1;
    if (!key.SignCompact(hash, &vchSig[1], rec))
        return false;
    assert(rec != -1);
    vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);
    return true;
}

bool CKey::Load(CPrivKey &privkey, CPubKey &vchPubKey, bool fSkipCheck=false) {
    CECKey key;
    if (!key.SetPrivKey(privkey, fSkipCheck))
        return false;
    
    key.GetSecretBytes(vch);
    fCompressed = vchPubKey.IsCompressed();
    fValid = true;
    
    if (fSkipCheck)
        return true;
    
    if (GetPubKey() != vchPubKey)
        return false;
    
    return true;
}

bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
    if (!IsValid())
        return false;
    CECKey key;
    if (!key.SetPubKey(*this))
        return false;
    if (!key.Verify(hash, vchSig))
        return false;
    return true;
}

bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
    if (vchSig.size() != 65)
        return false;
    CECKey key;
    if (!key.Recover(hash, &vchSig[1], (vchSig[0] - 27) & ~4))
        return false;
    key.GetPubKey(*this, (vchSig[0] - 27) & 4);
    return true;
}

bool CPubKey::IsFullyValid() const {
    if (!IsValid())
        return false;
    CECKey key;
    if (!key.SetPubKey(*this))
        return false;
    return true;
}

bool CPubKey::Decompress() {
    if (!IsValid())
        return false;
    CECKey key;
    if (!key.SetPubKey(*this))
        return false;
    key.GetPubKey(*this, false);
    return true;
}

void static BIP32Hash(const unsigned char chainCode[32], unsigned int nChild, unsigned char header, const unsigned char data[32], unsigned char output[64]) {
    unsigned char num[4];
    num[0] = (nChild >> 24) & 0xFF;
    num[1] = (nChild >> 16) & 0xFF;
    num[2] = (nChild >>  8) & 0xFF;
    num[3] = (nChild >>  0) & 0xFF;
    HMAC_SHA512_CTX ctx;
    HMAC_SHA512_Init(&ctx, chainCode, 32);
    HMAC_SHA512_Update(&ctx, &header, 1);
    HMAC_SHA512_Update(&ctx, data, 32);
    HMAC_SHA512_Update(&ctx, num, 4);
    HMAC_SHA512_Final(output, &ctx);
}

bool CKey::Derive(CKey& keyChild, unsigned char ccChild[32], unsigned int nChild, const unsigned char cc[32]) const {
    assert(IsValid());
    assert(IsCompressed());
    unsigned char out[64];
    LockObject(out);
    if ((nChild >> 31) == 0) {
        CPubKey pubkey = GetPubKey();
        assert(pubkey.begin() + 33 == pubkey.end());
        BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, out);
    } else {
        assert(begin() + 32 == end());
        BIP32Hash(cc, nChild, 0, begin(), out);
    }
    memcpy(ccChild, out+32, 32);
    bool ret = CECKey::TweakSecret((unsigned char*)keyChild.begin(), begin(), out);
    UnlockObject(out);
    keyChild.fCompressed = true;
    keyChild.fValid = ret;
    return ret;
}

bool CPubKey::Derive(CPubKey& pubkeyChild, unsigned char ccChild[32], unsigned int nChild, const unsigned char cc[32]) const {
    assert(IsValid());
    assert((nChild >> 31) == 0);
    assert(begin() + 33 == end());
    unsigned char out[64];
    BIP32Hash(cc, nChild, *begin(), begin()+1, out);
    memcpy(ccChild, out+32, 32);
    CECKey key;
    bool ret = key.SetPubKey(*this);
    ret &= key.TweakPublic(out);
    key.GetPubKey(pubkeyChild, true);
    return ret;
}

bool CExtKey::Derive(CExtKey &out, unsigned int nChild) const {
    out.nDepth = nDepth + 1;
    CKeyID id = key.GetPubKey().GetID();
    memcpy(&out.vchFingerprint[0], &id, 4);
    out.nChild = nChild;
    return key.Derive(out.key, out.vchChainCode, nChild, vchChainCode);
}

void CExtKey::SetMaster(const unsigned char *seed, unsigned int nSeedLen) {
    static const char hashkey[] = {'B','i','t','c','o','i','n',' ','s','e','e','d'};
    HMAC_SHA512_CTX ctx;
    HMAC_SHA512_Init(&ctx, hashkey, sizeof(hashkey));
    HMAC_SHA512_Update(&ctx, seed, nSeedLen);
    unsigned char out[64];
    LockObject(out);
    HMAC_SHA512_Final(out, &ctx);
    key.Set(&out[0], &out[32], true);
    memcpy(vchChainCode, &out[32], 32);
    UnlockObject(out);
    nDepth = 0;
    nChild = 0;
    memset(vchFingerprint, 0, sizeof(vchFingerprint));
}

CExtPubKey CExtKey::Neuter() const {
    CExtPubKey ret;
    ret.nDepth = nDepth;
    memcpy(&ret.vchFingerprint[0], &vchFingerprint[0], 4);
    ret.nChild = nChild;
    ret.pubkey = key.GetPubKey();
    memcpy(&ret.vchChainCode[0], &vchChainCode[0], 32);
    return ret;
}

void CExtKey::Encode(unsigned char code[74]) const {
    code[0] = nDepth;
    memcpy(code+1, vchFingerprint, 4);
    code[5] = (nChild >> 24) & 0xFF; code[6] = (nChild >> 16) & 0xFF;
    code[7] = (nChild >>  8) & 0xFF; code[8] = (nChild >>  0) & 0xFF;
    memcpy(code+9, vchChainCode, 32);
    code[41] = 0;
    assert(key.size() == 32);
    memcpy(code+42, key.begin(), 32);
}

void CExtKey::Decode(const unsigned char code[74]) {
    nDepth = code[0];
    memcpy(vchFingerprint, code+1, 4);
    nChild = (code[5] << 24) | (code[6] << 16) | (code[7] << 8) | code[8];
    memcpy(vchChainCode, code+9, 32);
    key.Set(code+42, code+74, true);
}

void CExtPubKey::Encode(unsigned char code[74]) const {
    code[0] = nDepth;
    memcpy(code+1, vchFingerprint, 4);
    code[5] = (nChild >> 24) & 0xFF; code[6] = (nChild >> 16) & 0xFF;
    code[7] = (nChild >>  8) & 0xFF; code[8] = (nChild >>  0) & 0xFF;
    memcpy(code+9, vchChainCode, 32);
    assert(pubkey.size() == 33);
    memcpy(code+41, pubkey.begin(), 33);
}

void CExtPubKey::Decode(const unsigned char code[74]) {
    nDepth = code[0];
    memcpy(vchFingerprint, code+1, 4);
    nChild = (code[5] << 24) | (code[6] << 16) | (code[7] << 8) | code[8];
    memcpy(vchChainCode, code+9, 32);
    pubkey.Set(code+41, code+74);
}

bool CExtPubKey::Derive(CExtPubKey &out, unsigned int nChild) const {
    out.nDepth = nDepth + 1;
    CKeyID id = pubkey.GetID();
    memcpy(&out.vchFingerprint[0], &id, 4);
    out.nChild = nChild;
    return pubkey.Derive(out.pubkey, out.vchChainCode, nChild, vchChainCode);
}