src/key.h

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2015 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_KEY_H
#define BITCOIN_KEY_H

#include "pubkey.h"
#include "serialize.h"
#include "support/allocators/secure.h"
#include "uint256.h"

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


/** 
 * secp256k1:
 * const unsigned int PRIVATE_KEY_SIZE = 279;
 * const unsigned int PUBLIC_KEY_SIZE  = 65;
 * const unsigned int SIGNATURE_SIZE   = 72;
 *
 * see www.keylength.com
 * script supports up to 75 for single byte push
 */

/**
 * secure_allocator is defined in allocators.h
 * CPrivKey is a serialized private key, with all parameters included (279 bytes)
 */
typedef std::vector<unsigned char, secure_allocator<unsigned char> > CPrivKey;

/** An encapsulated private key. */
class CKey
{
private:
    //! Whether this private key is valid. We check for correctness when modifying the key
    //! data, so fValid should always correspond to the actual state.
    bool fValid;

    //! Whether the public key corresponding to this private key is (to be) compressed.
    bool fCompressed;

    //! The actual byte data
    unsigned char vch[32];

    //! Check whether the 32-byte array pointed to be vch is valid keydata.
    bool static Check(const unsigned char* vch);

public:
    //! Construct an invalid private key.
    CKey() : fValid(false), fCompressed(false)
    {
        LockObject(vch);
    }

    //! Copy constructor. This is necessary because of memlocking.
    CKey(const CKey& secret) : fValid(secret.fValid), fCompressed(secret.fCompressed)
    {
        LockObject(vch);
        memcpy(vch, secret.vch, sizeof(vch));
    }

    //! Destructor (again necessary because of memlocking).
    ~CKey()
    {
        UnlockObject(vch);
    }

    friend bool operator==(const CKey& a, const CKey& b)
    {
        return a.fCompressed == b.fCompressed && a.size() == b.size() &&
               memcmp(&a.vch[0], &b.vch[0], a.size()) == 0;
    }

    //! Initialize using begin and end iterators to byte data.
    template <typename T>
    void Set(const T pbegin, const T pend, bool fCompressedIn)
    {
        if (pend - pbegin != 32) {
            fValid = false;
            return;
        }
        if (Check(&pbegin[0])) {
            memcpy(vch, (unsigned char*)&pbegin[0], 32);
            fValid = true;
            fCompressed = fCompressedIn;
        } else {
            fValid = false;
        }
    }

    //! Simple read-only vector-like interface.
    unsigned int size() const { return (fValid ? 32 : 0); }
    const unsigned char* begin() const { return vch; }
    const unsigned char* end() const { return vch + size(); }

    //! Check whether this private key is valid.
    bool IsValid() const { return fValid; }

    //! Check whether the public key corresponding to this private key is (to be) compressed.
    bool IsCompressed() const { return fCompressed; }

    //! Initialize from a CPrivKey (serialized OpenSSL private key data).
    bool SetPrivKey(const CPrivKey& vchPrivKey, bool fCompressed);

    //! Generate a new private key using a cryptographic PRNG.
    void MakeNewKey(bool fCompressed);

    /**
     * Convert the private key to a CPrivKey (serialized OpenSSL private key data).
     * This is expensive. 
     */
    CPrivKey GetPrivKey() const;

    /**
     * Compute the public key from a private key.
     * This is expensive.
     */
    CPubKey GetPubKey() const;

    /**
     * Create a DER-serialized signature.
     * The test_case parameter tweaks the deterministic nonce.
     */
    bool Sign(const uint256& hash, std::vector<unsigned char>& vchSig, uint32_t test_case = 0) const;

    /**
     * Create a compact signature (65 bytes), which allows reconstructing the used public key.
     * The format is one header byte, followed by two times 32 bytes for the serialized r and s values.
     * The header byte: 0x1B = first key with even y, 0x1C = first key with odd y,
     *                  0x1D = second key with even y, 0x1E = second key with odd y,
     *                  add 0x04 for compressed keys.
     */
    bool SignCompact(const uint256& hash, std::vector<unsigned char>& vchSig) const;

    //! Derive BIP32 child key.
    bool Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;

    /**
     * Verify thoroughly whether a private key and a public key match.
     * This is done using a different mechanism than just regenerating it.
     */
    bool VerifyPubKey(const CPubKey& vchPubKey) const;

    //! Load private key and check that public key matches.
    bool Load(CPrivKey& privkey, CPubKey& vchPubKey, bool fSkipCheck);

    //! Check whether an element of a signature (r or s) is valid.
    static bool CheckSignatureElement(const unsigned char* vch, int len, bool half);
};

struct CExtKey {
    unsigned char nDepth;
    unsigned char vchFingerprint[4];
    unsigned int nChild;
    ChainCode chaincode;
    CKey key;

    friend bool operator==(const CExtKey& a, const CExtKey& b)
    {
        return a.nDepth == b.nDepth && memcmp(&a.vchFingerprint[0], &b.vchFingerprint[0], 4) == 0 && a.nChild == b.nChild &&
               a.chaincode == b.chaincode && a.key == b.key;
    }

    void Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const;
    void Decode(const unsigned char code[BIP32_EXTKEY_SIZE]);
    bool Derive(CExtKey& out, unsigned int nChild) const;
    CExtPubKey Neuter() const;
    void SetMaster(const unsigned char* seed, unsigned int nSeedLen);
    template <typename Stream>
    void Serialize(Stream& s, int nType, int nVersion) const
    {
        unsigned int len = BIP32_EXTKEY_SIZE;
        ::WriteCompactSize(s, len);
        unsigned char code[BIP32_EXTKEY_SIZE];
        Encode(code);
        s.write((const char *)&code[0], len);
    }
    template <typename Stream>
    void Unserialize(Stream& s, int nType, int nVersion)
    {
        unsigned int len = ::ReadCompactSize(s);
        unsigned char code[BIP32_EXTKEY_SIZE];
        s.read((char *)&code[0], len);
        Decode(code);
    }
};

/** Initialize the elliptic curve support. May not be called twice without calling ECC_Stop first. */
void ECC_Start(void);

/** Deinitialize the elliptic curve support. No-op if ECC_Start wasn't called first. */
void ECC_Stop(void);

/** Check that required EC support is available at runtime. */
bool ECC_InitSanityCheck(void);

/** Generate a private key from just the secret parameter. */
int EC_KEY_regenerate_key(EC_KEY *eckey, BIGNUM *priv_key);

/** 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);

// 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);
    }

    EC_KEY* GetECKey() {
        return 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]) {
        BIGNUM bn;
        BN_init(&bn);
        assert(BN_bin2bn(vch, 32, &bn));
        assert(EC_KEY_regenerate_key(pkey, &bn));
        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;
    }
};

#endif // BITCOIN_KEY_H