From 6d169425d1609a564c6c1f2fb8f4e8d59e896e50 Mon Sep 17 00:00:00 2001
From: Jack Robison <jackrobison@lbry.io>
Date: Mon, 27 Nov 2017 10:24:10 -0500
Subject: [PATCH] split b58 checksum validation from address validation

---
 address/base58/character.go |  5 ++---
 address/base58/checksum.go  | 20 ++++++++++++++++++++
 address/base58/decode.go    |  7 +++++--
 address/base58/encode.go    |  4 ++--
 address/decode.go           |  1 +
 address/validate.go         | 19 ++++---------------
 6 files changed, 34 insertions(+), 22 deletions(-)
 create mode 100644 address/base58/checksum.go

diff --git a/address/base58/character.go b/address/base58/character.go
index 82adb0d..cc9a78c 100644
--- a/address/base58/character.go
+++ b/address/base58/character.go
@@ -1,17 +1,16 @@
 package base58
 
 import (
-	"math/big"
 	"errors"
+	"math/big"
 )
 
-var b58_characters = [58]byte {0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x41, 0x42, 0x43, 0x44, 0x45,
+var b58_characters = [58]byte{0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x41, 0x42, 0x43, 0x44, 0x45,
 	0x46, 0x47, 0x48, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55,
 	0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
 	0x6a, 0x6b, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
 	0x79, 0x7a}
 
-
 func CharacterIndex(character byte) (*big.Int, error) {
 	for i := 0; i < 58; i++ {
 		if b58_characters[i] == character {
diff --git a/address/base58/checksum.go b/address/base58/checksum.go
new file mode 100644
index 0000000..de115c1
--- /dev/null
+++ b/address/base58/checksum.go
@@ -0,0 +1,20 @@
+package base58
+
+import "crypto/sha256"
+
+const checksum_length = 4
+
+func VerifyBase58Checksum(v []byte) bool {
+	checksum := [checksum_length]byte{}
+	for i := range checksum {
+		checksum[i] = v[len(v)-checksum_length+i]
+	}
+	real_checksum := sha256.Sum256(v[:len(v)-checksum_length])
+	real_checksum = sha256.Sum256(real_checksum[:])
+	for i, c := range checksum {
+		if c != real_checksum[i] {
+			return false
+		}
+	}
+	return true
+}
diff --git a/address/base58/decode.go b/address/base58/decode.go
index 46dd65f..d0854f1 100644
--- a/address/base58/decode.go
+++ b/address/base58/decode.go
@@ -1,8 +1,8 @@
 package base58
 
 import (
-	"math/big"
 	"errors"
+	"math/big"
 )
 
 func DecodeBase58(value string, size int64) ([]byte, error) {
@@ -12,7 +12,7 @@ func DecodeBase58(value string, size int64) ([]byte, error) {
 	for i := int64(len(buf) - 1); i >= 0; i-- {
 		to_add := big.NewInt(0)
 		to_add = to_add.Exp(big.NewInt(58), big.NewInt(i), to_add)
-		c, err := CharacterIndex(buf[int64(len(buf)) - i - 1])
+		c, err := CharacterIndex(buf[int64(len(buf))-i-1])
 		if err != nil {
 			return result, err
 		}
@@ -32,5 +32,8 @@ func DecodeBase58(value string, size int64) ([]byte, error) {
 	if long_value.Int64() != 0 {
 		return result, errors.New("cannot decode to the given size")
 	}
+	if size != int64(len(result)) {
+		return result, errors.New("length mismatch")
+	}
 	return result, nil
 }
diff --git a/address/base58/encode.go b/address/base58/encode.go
index 12eeafa..a0f86b6 100644
--- a/address/base58/encode.go
+++ b/address/base58/encode.go
@@ -4,13 +4,13 @@ import (
 	"math/big"
 )
 
-func EncodeBase58(data []byte) (string) {
+func EncodeBase58(data []byte) string {
 	long_value := big.NewInt(0)
 	result := ""
 	for i := 0; i < len(data); i++ {
 		to_add := big.NewInt(0)
 		to_add = to_add.Exp(big.NewInt(256), big.NewInt(int64(i)), to_add)
-		to_add = to_add.Mul(big.NewInt(int64(data[24 - i])), to_add)
+		to_add = to_add.Mul(big.NewInt(int64(data[24-i])), to_add)
 		long_value = long_value.Add(to_add, long_value)
 	}
 	i := 0
diff --git a/address/decode.go b/address/decode.go
index 6d244fa..73789e1 100644
--- a/address/decode.go
+++ b/address/decode.go
@@ -14,5 +14,6 @@ func DecodeAddress(address string, blockchainName string) ([address_length]byte,
 	for i, b := range decoded {
 		buf[i] = b
 	}
+
 	return ValidateAddress(buf, blockchainName)
 }
diff --git a/address/validate.go b/address/validate.go
index 5b5a893..992e3f4 100644
--- a/address/validate.go
+++ b/address/validate.go
@@ -1,7 +1,7 @@
 package address
 
 import (
-	"crypto/sha256"
+	"./base58"
 	"errors"
 )
 
@@ -48,19 +48,8 @@ func PubKeyIsValid(address [address_length]byte) bool {
 	return true
 }
 
-func ChecksumIsValid(address [address_length]byte) bool {
-	checksum := [checksum_length]byte{}
-	for i := range checksum {
-		checksum[i] = address[prefix_length+pubkey_length+i]
-	}
-	real_checksum := sha256.Sum256(address[:prefix_length+pubkey_length])
-	real_checksum = sha256.Sum256(real_checksum[:])
-	for i, c := range checksum {
-		if c != real_checksum[i] {
-			return false
-		}
-	}
-	return true
+func AddressChecksumIsValid(address [address_length]byte) bool {
+	return base58.VerifyBase58Checksum(address[:])
 }
 
 func ValidateAddress(address [address_length]byte, blockchainName string) ([address_length]byte, error) {
@@ -73,7 +62,7 @@ func ValidateAddress(address [address_length]byte, blockchainName string) ([addr
 	if !PubKeyIsValid(address) {
 		return address, errors.New("invalid pubkey")
 	}
-	if !ChecksumIsValid(address) {
+	if !AddressChecksumIsValid(address) {
 		return address, errors.New("invalid address checksum")
 	}
 	return address, nil