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< / script > < / nav > < / div > < div class = "container mainContainer docsContainer" > < div class = "wrapper" > < div class = "post" > < header class = "postHeader" > < a class = "edit-page-link button" href = "https://github.com/bitcoin-s/bitcoin-s/blob/master/docs/secp256k1/secp256k1.md" target = "_blank" rel = "noreferrer noopener" > Edit< / a > < h1 id = "__docusaurus" class = "postHeaderTitle" > Secp256k1< / h1 > < / header > < article > < div > < span > < p > < a href = "https://github.com/bitcoin-core/secp256k1" > Libsecp256k1< / a > is used to preform cryptographic operations on the secp256k1 curve.
This is the curve that bitcoin uses. There is a < em > signficant< / em > speedup when using this library compared to java crypto libraries
like bouncy castle.< / p >
< p > In bitcoin-s, we support native binaries for libsecp256k1< / p >
< ol >
< li > < a href = "../../secp256k1jni/natives/linux_32" > linux 32 bit< / a > < / li >
< li > < a href = "../../secp256k1jni/natives/linux_64" > linux 64 bit< / a > < / li >
< li > < a href = "../../secp256k1jni/natives/osx_64" > mac osx 64 bit< / a > < / li >
< li > < a href = "../../secp256k1jni/natives/windows_64" > windows 64 bit< / a > < / li >
< / ol >
< p > Bitcoin-s uses a zero dependency library called < a href = "https://github.com/scijava/native-lib-loader" > < code > native-lib-loader< / code > < / a > .
That does the appropriate loading of the library onto your classpath to be accessed.< / p >
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< h3 > < a class = "anchor" aria-hidden = "true" id = "using-libsecp256k1" > < / a > < a href = "#using-libsecp256k1" aria-hidden = "true" class = "hash-link" > < svg class = "hash-link-icon" aria-hidden = "true" height = "16" version = "1.1" viewBox = "0 0 16 16" width = "16" > < path fill-rule = "evenodd" d = "M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z" > < / path > < / svg > < / a > Using libsecp256k1< / h3 >
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< p > To tell if you have access to libsecp256k1 you can do the following< / p >
< pre > < code class = "hljs css language-scala" > < span class = "hljs-keyword" > val< / span > isEnabled = org.bitcoin.< span class = "hljs-type" > Secp256k1Context< / span > .isEnabled()
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println(< span class = "hljs-string" > s"Secp256k1Context.isEnabled=< span class = "hljs-subst" > ${isEnabled}< / span > "< / span > )
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< / code > < / pre >
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< p > If libsecp256k1 is enabled, you can use < a href = "/api/org/bitcoin/NativeSecp256k1" > NativeSecp256k1< / a >
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with static method defined in the class.< / p >
< pre > < code class = "hljs css language-scala" > < span class = "hljs-keyword" > val< / span > privKey = < span class = "hljs-type" > ECPrivateKey< / span > .freshPrivateKey
< span class = "hljs-keyword" > val< / span > pubKey = privKey.publicKey
< span class = "hljs-keyword" > val< / span > dataToSign = < span class = "hljs-type" > DoubleSha256Digest< / span > .empty
< span class = "hljs-keyword" > val< / span > signature = < span class = "hljs-type" > NativeSecp256k1< / span > .sign(dataToSign.bytes.toArray, privKey.bytes.toArray)
< span class = "hljs-keyword" > val< / span > verify = < span class = "hljs-type" > NativeSecp256k1< / span > .verify(dataToSign.bytes.toArray, signature, pubKey.bytes.toArray)
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println(< span class = "hljs-string" > s"Verified with NativeSecp256k1 signature=< span class = "hljs-subst" > ${verify}< / span > "< / span > )
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< span class = "hljs-comment" > //you can also just directly sign with the ECKey interface:< / span >
< span class = "hljs-keyword" > val< / span > signature2 = privKey.sign(dataToSign)
< span class = "hljs-keyword" > val< / span > verified2 = pubKey.verify(dataToSign, signature2)
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println(< span class = "hljs-string" > s"Verified with NativeSecp256k1 again=< span class = "hljs-subst" > ${verified2}< / span > "< / span > )
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< / code > < / pre >
< h3 > < a class = "anchor" aria-hidden = "true" id = "when-libsecp256k1-isnt-available-or-you-want-to-turn-it-off" > < / a > < a href = "#when-libsecp256k1-isnt-available-or-you-want-to-turn-it-off" aria-hidden = "true" class = "hash-link" > < svg class = "hash-link-icon" aria-hidden = "true" height = "16" version = "1.1" viewBox = "0 0 16 16" width = "16" > < path fill-rule = "evenodd" d = "M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z" > < / path > < / svg > < / a > When libsecp256k1 isn't available, or you want to turn it off< / h3 >
< p > There are two reasons you wouldn't want to use libsecp256k1< / p >
< ol >
< li > You don't trust the pre-compiled binaries we are using< / li >
< li > Your OS/arch is not supported< / li >
< / ol >
< p > There are two ways you can circumvent libsecp256k1< / p >
< ol >
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< li > Set < code > DISABLE_SECP256K1=true< / code > in your environment variables. This will force < code > CryptoContext.default< / code > to return false which will make Bitcoin-S act like < code > Secp256k1Context.isEnabled()< / code > has returned false.< / li >
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< li > Call Bouncy castle methods in < code > ECKey< / code > .< / li >
< / ol >
< p > Here is an example of calling bouncy castle methods in < code > ECKey< / code > < / p >
< pre > < code class = "hljs css language-scala" > < span class = "hljs-keyword" > val< / span > privKey = < span class = "hljs-type" > ECPrivateKey< / span > .freshPrivateKey
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< span class = "hljs-comment" > // privKey: ECPrivateKey = Masked(ECPrivateKey)< / span >
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< span class = "hljs-comment" > // calls bouncy castle indirectly via CryptoContext< / span >
< span class = "hljs-keyword" > val< / span > publicKey = privKey.publicKey
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< span class = "hljs-comment" > // publicKey: ECPublicKey = ECPublicKey(023c0374e38d9c2bfef4cd87556a690794267957775569ba7bc51498aafef90511)< / span >
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< span class = "hljs-keyword" > val< / span > dataToSign = < span class = "hljs-type" > DoubleSha256Digest< / span > .empty
< span class = "hljs-comment" > // dataToSign: DoubleSha256Digest = DoubleSha256Digest(0000000000000000000000000000000000000000000000000000000000000000)< / span >
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< span class = "hljs-comment" > // calls bouncy castle indirectly via CryptoContext< / span >
< span class = "hljs-keyword" > val< / span > signature = privKey.sign(dataToSign.bytes)
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< span class = "hljs-comment" > // signature: ECDigitalSignature = ECDigitalSignature(3045022100d7828c6aa61a5d4bad3a8720780b1a9db12419467f766f9d76f9c2d5166b0ed60220261857274cc5c634f5ff2eb2f806145d396590a2ac5f58ad6c83dd2edb613de6)< / span >
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< span class = "hljs-comment" > // calls bouncy castle indirectly via CryptoContext< / span >
< span class = "hljs-keyword" > val< / span > verified = publicKey.verify(dataToSign.bytes, signature)
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< span class = "hljs-comment" > // verified: Boolean = true< / span >
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println(< span class = "hljs-string" > s"Verified with bouncy castle=< span class = "hljs-subst" > ${verified}< / span > "< / span > )
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< span class = "hljs-comment" > // Verified with bouncy castle=true< / span >
< / code > < / pre >
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< h3 > < a class = "anchor" aria-hidden = "true" id = "building-libsecp256k1" > < / a > < a href = "#building-libsecp256k1" aria-hidden = "true" class = "hash-link" > < svg class = "hash-link-icon" aria-hidden = "true" height = "16" version = "1.1" viewBox = "0 0 16 16" width = "16" > < path fill-rule = "evenodd" d = "M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z" > < / path > < / svg > < / a > Building libsecp256k1< / h3 >
< p > < a href = "/docs/next/secp256k1/jni-modify#adding-to-bitcoin-s" > See instructions here< / a > < / p >
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