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Bitcoin digital signing is the other big thing aside from the blockchain. Every digital wallet has the capability to sign arbitary messages using a private key secretly embedded in the wallet. Anyone who knows the Bitcoin address which had been created from the private key can verify the signed messages. This is also true with Denarius and Bitcoin-based Altcoins.
A Bitcoin address is created from the public key of the private-public key pair generated within the wallet. Only those who have the private key can sign the message. The owner of a Bitcoin address will do his best to keep its private key secret. Otherwise, his Bitcoin values may be gone. Thus, a signing verification will safely proof that the owner of the address had signed the message himself.
The Bitcoin public key cryptography is based on Elliptic Curve Digital Signature Algorithm (ECDSA). It uses elliptic-curve cryptography (ECC).
ECDSA vs RSA
A snippet from a blog post ECDSA: The digital signature algorithm of a better internet by Nick Sullivan:
Why is ECDSA the algorithm of choice for new protocols when RSA is available and has been the gold standard for asymmetric cryptography since 1977? It boils down to the fact that we are better at breaking RSA than we are at breaking ECC.
As we described in a previous blog post, the security of a key depends on its size and its algorithm. Some algorithms are easier to break than others and require larger keys for the same level of security. Breaking an RSA key requires you to factor a large number. We are pretty good at factoring large numbers and getting better all the time. Breaking an ECDSA key requires you to solve the Elliptic Curve Discrete Logarithm Problem (ECDLP). The mathematical community has not made any major progress in improving algorithms to solve this problem since is was independently introduced by Koblitz and Miller in 1985.
This means that with ECDSA you can get the same level of security as RSA but with smaller keys. Smaller keys are better than larger keys for several reasons. Smaller keys have faster algorithms for generating signatures because the math involves smaller numbers. Smaller public keys mean smaller certificates and less data to pass around to establish a TLS connection. This means quicker connections and faster loading times on websites.
PHP Implementation
The verification of a signed message doesn't have to be done within a wallet. This PHP script implements the algorithm to digitally verify signed messages from Bitcoin, Denarius and Bitcoin-based Altcoins. Denarius is a Bitcoin-based Altcoin.
C++ Implementation
Here is the one implemented in C++ https://github.com/chelahmy/dnrverify extracted from the original Bitcoin code.
php 5.4.0 or newer.
php5-gmp needs to be installed.
Instantiation
use AltcoinsECDSA\AltcoinsECDSA;
require_once("src/AltcoinsECDSA.php");
$bitcoinECDSA = new AltcoinsECDSA();for Denarius
$altcoinECDSA = new AltcoinsECDSA('DNR');Set a private key
$altcoinECDSA->setPrivateKey($k);examples of private keys :
4C28FCA386C7A227600B2FE50B7CAE11EC86D3BF1FBE471BE89827E19D72AA1D 00FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC
Generate a random private key
$altcoinECDSA->generateRandomPrivateKey($nonce);The nonce is optional, typically the nonce is a chunck of random data you get from the user. This can be mouse coordinates. Using a nonce adds randomness, which means the generated private key is stronger.
Get the private key
$altcoinECDSA->getPrivateKey();Returns the private key.
Get the Wif
$altcoinECDSA->getWif();returns the private key under the Wallet Import Format
Get the Public Key
$altcoinECDSA->getPubKey();Returns the compressed public key. The compressed PubKey starts with 0x02 if it's y coordinate is even and 0x03 if it's odd, the next 32 bytes corresponds to the x coordinates.
Example : 0226c50013603b085fbc26411d5d7e564b252d88964eedc4e01251d2d495e92c29
Get the Uncompressed Public Key
$altcoinECDSA->getUncompressedPubKey();Returns the The uncompressed PubKey. The uncompressed PubKey starts with 0x04, the next 32 bytes are the x coordinates, the last 32 bytes are the y coordinates.
Example : 04c80e8af3f1b7816a18aa24f242fc0740e9c4027d67c76dacf4ce32d2e5aace241c426fd288a9976ca750f1b192d3acd89dfbeca07ef27f3e5eb5d482354c4249
Get the coordinates of the Public Key
$altcoinECDSA->getPubKeyPoints();Returns an array containing the x and y coordinates of the public key
Example : Array ( [x] => a69243f3c4c047aba38d7ac3660317629c957ab1f89ea42343aee186538a34f8 [y] => b6d862f39819060378542a3bb43ff76b5d7bb23fc012f09c3cd2724bebe0b0bd )
Get the Address
$altcoinECDSA->getAddress();Returns the compressed Bitcoin Address.
Get the uncompressed Address
$altcoinECDSA->getUncompressedAddress();Returns the uncompressed Bitcoin Address.
Validate an address
$altcoinECDSA->validateAddress($address);Returns true if the address is valid and false if it isn't
Validate a Wif key
$altcoinECDSA->validateWifKey($wif);Returns true if the WIF key is valid and false if it isn't
Sign a message
$altcoinECDSA->signMessage('message');Returns a satoshi client standard signed message.
verify a message
$altcoinECDSA->checkSignatureForRawMessage($signedMessage);Returns true if the signature is matching the address and false if it isn't.
sign a sha256 hash
$altcoinECDSA->signHash($hash);Returns a DER encoded hexadecimal signature.
verify a signature
$altcoinECDSA->checkDerSignature($pubKey, $signature, $hash)Returns true if the signature is matching the public key and false if it isn't.
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