secp256k1 Sign & Verify (Sample: https://runkit.com/wietsewind/5c6abbb0549f4e0012a665d5)

index.js

const elliptic = require('elliptic')
const secp256k1 = elliptic.ec('secp256k1')
const hash = require('hash.js')
const keypairs = require('ripple-keypairs')

const hexToDecimal = (x) => secp256k1.keyFromPrivate(x, 'hex').getPrivate().toString(10)

module.exports = {
    sign (message, familySeed) {
        const digest = hash.sha256().update(message).digest('hex').toUpperCase()
        const keypair = keypairs.deriveKeypair(familySeed)
        const signature = secp256k1.sign(digest, keypair.privateKey.substr(2))
        return {
            hash: digest,
            signature: (signature.r.toJSON() + signature.s.toJSON() + signature.recoveryParam.toString(16)).toUpperCase()
        }
    },
    unserializeSignature (signature) {
        return {
            r: signature.slice(0, 64).toLowerCase(),
            s: signature.slice(64, 128).toLowerCase(),
            recoveryParam: parseInt(signature.slice(128), 16)
        }
    },
    deriveAddress (familySeed) {
        const keypair = keypairs.deriveKeypair(familySeed)
        return keypairs.deriveAddress(keypair.publicKey)
    },
    recoverPubKey (hash, signature) {
        const unserializedSignature = this.unserializeSignature(signature)
        const pubKeyRecovered = secp256k1.recoverPubKey(hexToDecimal(hash), unserializedSignature, unserializedSignature.recoveryParam, 'hex')
        return pubKeyRecovered
    },
    recoverAddress (hash, signature) {
        return keypairs.deriveAddress(this.recoverPubKey(hash, signature).encodeCompressed('hex'))
    },
    verify (message, signature) {
        const digest = hash.sha256().update(message).digest('hex')
        const unserializedSignature = this.unserializeSignature(signature)
        return secp256k1.verify(digest, unserializedSignature, this.recoverPubKey(digest, signature))
    }
}

sample.js

const sampleLib = require('./')

const familySeed = 'spyWUG5bB6UPURokVDQsj2jceSwsD'
const message = 'This is me testing :)'

const account = sampleLib.deriveAddress(familySeed)
const signed = sampleLib.sign(message, familySeed)
const accountFromSignature = sampleLib.recoverAddress(signed.hash, signed.signature)
const verified = sampleLib.verify(message, signed.signature)

console.log(`
    Account:                 ${account}
    Message Hash:            ${signed.hash}
    Signature:               ${signed.signature}
    Account from Signature:  ${accountFromSignature}
    Signature Valid for Msg: ${verified}
`)

Sample output:

Account:                 rUwHCiUJJwxYU9Bjc8EmHCRnvh4rJgHN2A
Message Hash:            D65CC5390FAD02D43CD64F931EA47E06D7EFA1A5FD0DB32CB719FAE67CBBD525
Signature:               B1366626C0FED1A5169D96A4C9975A4E416B3B1CB236E972CD2BCCA033F38E76BB0882E02BF041015AC36C2A2C1B570A728BDB251528864544FF68395667D8760
Account from Signature:  rUwHCiUJJwxYU9Bjc8EmHCRnvh4rJgHN2A
Signature Valid for Msg: true