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hashcash a Go library which implements the hashcash proof-of-work algorithm.

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Hashcash

Hashcash is a Go library which implements the hashcash algorithm. Hashcash is a proof-of-work algorithm, which has been used as a denial-of-service counter measure technique in a number of systems. To learn more about hashcash, go here.

Installation

go get github.com/umahmood/hashcash

Usage

Computing a hashcash:

package main

import (
    "fmt"
    
    "github.com/umahmood/hashcash"
)

func validateResource(resource string) bool {
    // validate resource. resource could be an email, ip 
    // address, etc... so for an email we could check it 
    // exists in the database.
    return true
}

func main() {
    hc, err := hashcash.New(
        &hashcash.Resource{
            Data:          "[email protected]",
            ValidatorFunc: validateResource,
        },
        nil, // use default config.
    )
    if err != nil {
        // handle error
    }
    
    solution, err := hc.Compute()
    if err != nil {
        if err != hashcash.ErrSolutionFail {
            // did not find a solution, can call compute again.
        }
    } 
    fmt.Println(solution)
}

Output:

1:20:040806:foo::65f460d0726f420d:13a6b8
$ echo -n "1:20:040806:foo::65f460d0726f420d:13a6b8" | shasum
00000f91d51a9c213f9b7420c35c62b5e818c23e

Verifying a hashcash:

valid, err := hc.Verify(solution)
if err != nil {
    // handle error
}
if !valid {
   // hashcash token failed verification.
}

Storage:

In order to detect double spending, hashcash stores verified hashcash tokens in a sqlite3 database. This database is stored in ~/.hashcash/spent.db.

If you would like to change the underlying storage (i.e. to an in memory hash table) or location. You will need to build a type which satisfies the Storage interface.

To Do

  • Allow entries in default storage (sqlite3 database) to be purged.

Documentation

http://godoc.org/github.com/umahmood/hashcash

License

See the LICENSE file for license rights and limitations (MIT).

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