func (c *TLSEcdheEcdsaWithAes256CbcSha) Init(masterSecret, clientRandom, serverRandom []byte, isClient bool) error {
	const (
		prfMacLen = 20
		prfKeyLen = 32
		prfIvLen  = 16
	)
	keys, err := prf.GenerateEncryptionKeys(masterSecret, clientRandom, serverRandom, prfMacLen, prfKeyLen, prfIvLen, c.HashFunc())
	if err != nil {
		return err
	}
	var cbc *ciphersuite.CBC
	if isClient {
		cbc, err = ciphersuite.NewCBC(
			keys.ClientWriteKey, keys.ClientWriteIV, keys.ClientMACKey,
			keys.ServerWriteKey, keys.ServerWriteIV, keys.ServerMACKey,
			sha1.New,
		)
	} else {
		cbc, err = ciphersuite.NewCBC(
			keys.ServerWriteKey, keys.ServerWriteIV, keys.ServerMACKey,
			keys.ClientWriteKey, keys.ClientWriteIV, keys.ClientMACKey,
			sha1.New,
		)
	}
	c.cbc.Store(cbc)
	return err
}
Init initializes the internal Cipher with keying material
package ciphersuite
import (
	"crypto/sha1"  
	"crypto/sha256"
	"fmt"
	"hash"
	"sync/atomic"
	"github.com/pion/dtls/v2/pkg/crypto/ciphersuite"
	"github.com/pion/dtls/v2/pkg/crypto/clientcertificate"
	"github.com/pion/dtls/v2/pkg/crypto/prf"
	"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
)
type TLSEcdheEcdsaWithAes256CbcSha struct {
	cbc atomic.Value  
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) CertificateType() clientcertificate.Type {
	return clientcertificate.ECDSASign
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) ID() ID {
	return TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) String() string {
	return "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA"
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) HashFunc() func() hash.Hash {
	return sha256.New
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) AuthenticationType() AuthenticationType {
	return AuthenticationTypeCertificate
}
func (c *TLSEcdheEcdsaWithAes256CbcSha) IsInitialized() bool {
	return c.cbc.Load() != nil
}