/src/key.cpp

// Copyright (c) 2009-2014 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 <openssl/ecdsa.h>
#include <openssl/rand.h>
#include <openssl/obj_mac.h>

#include "key.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]) {
        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) {
        const unsigned char* pbegin = &privkey[0];
        if (d2i_ECPrivateKey(&pkey, &pbegin, privkey.size())) {
            // 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) {
        unsigned int nSize = ECDSA_size(pkey);
        vchSig.resize(nSize); // Make sure it is big enough
        assert(ECDSA_sign(0, (unsigned char*)&hash, sizeof(hash), &vchSig[0], &nSize, pkey));
        vchSig.resize(nSize); // Shrink to fit actual size
        return true;
    }

    bool Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
        if (vchSig.empty())
            return false;

        // New versions of OpenSSL will reject non-canonical DER signatures. de/re-serialize first.
        unsigned char *norm_der = NULL;
        ECDSA_SIG *norm_sig = ECDSA_SIG_new();
        const unsigned char* sigptr = &vchSig[0];
        assert(norm_sig);
        if (d2i_ECDSA_SIG(&norm_sig, &sigptr, vchSig.size()) == NULL)
        {
            /* As of OpenSSL 1.0.0p d2i_ECDSA_SIG frees and nulls the pointer on
             * error. But OpenSSL's own use of this function redundantly frees the
             * result. As ECDSA_SIG_free(NULL) is a no-op, and in the absence of a
             * clear contract for the function behaving the same way is more
             * conservative.
             */
            ECDSA_SIG_free(norm_sig);
            return false;
        }
        int derlen = i2d_ECDSA_SIG(norm_sig, &norm_der);
        ECDSA_SIG_free(norm_sig);
        if (derlen <= 0)
            return false;

        // -1 = error, 0 = bad sig, 1 = good
        bool ret = ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), norm_der, derlen, pkey) == 1;
        OPENSSL_free(norm_der);
        return ret;
    }

    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;
    }
};

}; // end of anonymous namespace

bool CKey::Check(const unsigned char *vch) {
    // Do not convert to OpenSSL's data structures for range-checking keys,
    // it's easy enough to do directly.
    static const unsigned char vchMax[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
    };
    bool fIsZero = true;
    for (int i=0; i<32 && fIsZero; i++)
        if (vch[i] != 0)
            fIsZero = false;
    if (fIsZero)
        return false;
    for (int i=0; i<32; i++) {
        if (vch[i] < vchMax[i])
            return true;
        if (vch[i] > vchMax[i])
            return false;
    }
    return true;
}

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