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Merge pull request #36 from nicksavers/master 

Document ECKey and add credits to bitcoinj
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romanman 2014-06-23 09:55:14 +01:00
parent ce94a3f54f c342afcd84
commit 6cb8ecffbe
1 changed files with 30 additions and 13 deletions
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43
ethereumj-core/src/main/java/org/ethereum/crypto/ECKey.java
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@ -13,12 +13,6 @@ package org.ethereum.crypto;
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*
* www.ethereumJ.com
* @author: Nick Savers
* Created on: 20/05/2014 10:44
*
*/
import static org.ethereum.util.ByteUtil.bigIntegerToBytes;
@ -50,11 +44,34 @@ import org.spongycastle.math.ec.ECCurve;
import org.spongycastle.math.ec.ECPoint;
import org.spongycastle.util.encoders.Base64;
import org.spongycastle.util.encoders.Hex;
/**
* <p>Represents an elliptic curve public and (optionally) private key, usable for digital signatures but not encryption.
* Creating a new ECKey with the empty constructor will generate a new random keypair. Other static methods can be used
* when you already have the public or private parts. If you create a key with only the public part, you can check
* signatures but not create them.</p>
*
* <p>The ECDSA algorithm supports <i>key recovery</i> in which a signature plus a couple of discriminator bits can
* be reversed to find the public key used to calculate it. This can be convenient when you have a message and a
* signature and want to find out who signed it, rather than requiring the user to provide the expected identity.</p>
*
* <p>A key can be <i>compressed</i> or <i>uncompressed</i>. This refers to whether the public key is represented
* when encoded into bytes as an (x, y) coordinate on the elliptic curve, or whether it's represented as just an X
* co-ordinate and an extra byte that carries a sign bit. With the latter form the Y coordinate can be calculated
* dynamically, however, <b>because the binary serialization is different the address of a key changes if its
* compression status is changed</b>. If you deviate from the defaults it's important to understand this: money sent
* to a compressed version of the key will have a different address to the same key in uncompressed form. Whether
* a public key is compressed or not is recorded in the SEC binary serialisation format, and preserved in a flag in
* this class so round-tripping preserves state. Unless you're working with old software or doing unusual things, you
* can usually ignore the compressed/uncompressed distinction.</p>
*
* This code is borrowed from the bitcoinj project and altered to fit Ethereum.</br>
* See <a href="https://github.com/bitcoinj/bitcoinj/blob/master/core/src/main/java/com/google/bitcoin/core/ECKey.java">bitcoinj on GitHub</a>
*/
public class ECKey implements Serializable {
private static final Logger logger = LoggerFactory.getLogger(ECKey.class);
/** The parameters of the secp256k1 curve that Bitcoin uses. */
/** The parameters of the secp256k1 curve that Ethereum uses. */
public static final ECDomainParameters CURVE;
/**
@ -67,7 +84,7 @@ public class ECKey implements Serializable {
private static final long serialVersionUID = -728224901792295832L;
static {
// All clients must agree on the curve to use by agreement. Bitcoin uses secp256k1.
// All clients must agree on the curve to use by agreement. Ethereum uses secp256k1.
X9ECParameters params = SECNamedCurves.getByName("secp256k1");
CURVE = new ECDomainParameters(params.getCurve(), params.getG(), params.getN(), params.getH());
HALF_CURVE_ORDER = params.getN().shiftRight(1);
@ -278,8 +295,8 @@ public class ECKey implements Serializable {
}
/**
* Groups the two components that make up a signature, and provides a way to encode to DER form, which is
* how ECDSA signatures are represented when embedded in other data structures in the Bitcoin protocol. The raw
* Groups the two components that make up a signature, and provides a way to encode to Base64 form, which is
* how ECDSA signatures are represented when embedded in other data structures in the Ethereum protocol. The raw
* components can be useful for doing further EC maths on them.
*/
public static class ECDSASignature {
@ -308,7 +325,7 @@ public class ECKey implements Serializable {
/**
* Will automatically adjust the S component to be less than or equal to half the curve order, if necessary.
* This is required because for every signature (r,s) the signature (r, -s (mod N)) is a valid signature of
* the same message. However, we dislike the ability to modify the bits of a Bitcoin transaction after it's
* the same message. However, we dislike the ability to modify the bits of a Ethereum transaction after it's
* been signed, as that violates various assumed invariants. Thus in future only one of those forms will be
* considered legal and the other will be banned.
*/
@ -403,7 +420,7 @@ public class ECKey implements Serializable {
* determine if the signature was correct.
*
* @param message a piece of human readable text that was signed
* @param signatureBase64 The Bitcoin-format message signature in base64
* @param signatureBase64 The Ethereum-format message signature in base64
* @throws SignatureException If the public key could not be recovered or if there was a signature format error.
*/
public static ECKey signatureToKey(byte[] messageHash, String signatureBase64) throws SignatureException {