rsa数据加密无大小限制——golang实现

由于rsa加密需要公钥长度大于消息长度，消息太长时经常会报错Message too long for RSA
采用分块的方法，将消息分成更小的块，解决这个问题

package xrsa
import (
    "encoding/pem"
    "encoding/base64"
    "crypto/x509"
    "crypto/rsa"
    "crypto/rand"
    "errors"
    "crypto"
    "io"
    "bytes"
    "encoding/asn1"
)
const (
    CHAR_SET = "UTF-8"
    BASE_64_FORMAT = "UrlSafeNoPadding"
    RSA_ALGORITHM_KEY_TYPE = "PKCS8"
    RSA_ALGORITHM_SIGN = crypto.SHA256
)
type XRsa struct {
    publicKey *rsa.PublicKey
    privateKey *rsa.PrivateKey
}
// 生成密钥对
func CreateKeys(publicKeyWriter, privateKeyWriter io.Writer, keyLength int) error {
    // 生成私钥文件
    privateKey, err := rsa.GenerateKey(rand.Reader, keyLength)
    if err != nil {
        return err
    }
    derStream := MarshalPKCS8PrivateKey(privateKey)
    block := &pem.Block{
        Type:  "PRIVATE KEY",
        Bytes: derStream,
    }
    err = pem.Encode(privateKeyWriter, block)
    if err != nil {
        return err
    }
    // 生成公钥文件
    publicKey := &privateKey.PublicKey
    derPkix, err := x509.MarshalPKIXPublicKey(publicKey)
    if err != nil {
        return err
    }
    block = &pem.Block{
        Type:  "PUBLIC KEY",
        Bytes: derPkix,
    }
    err = pem.Encode(publicKeyWriter, block)
    if err != nil {
        return err
    }
    return nil
}
func NewXRsa(publicKey []byte, privateKey []byte) (*XRsa, error) {
    block, _ := pem.Decode(publicKey)
    if block == nil {
        return nil, errors.New("public key error")
    }
    pubInterface, err := x509.ParsePKIXPublicKey(block.Bytes)
    if err != nil {
        return nil, err
    }
    pub := pubInterface.(*rsa.PublicKey)
    block, _ = pem.Decode(privateKey)
    if block == nil {
        return nil, errors.New("private key error!")
    }
    priv, err := x509.ParsePKCS8PrivateKey(block.Bytes)
    if err != nil {
        return nil, err
    }
    pri, ok := priv.(*rsa.PrivateKey)
    if ok {
        return &XRsa {
            publicKey: pub,
            privateKey: pri,
        }, nil
    } else {
        return nil, errors.New("private key not supported")
    }
}
// 公钥加密
func (r *XRsa) PublicEncrypt(data string) (string, error) {
    partLen := r.publicKey.N.BitLen() / 8 - 11
    chunks := split([]byte(data), partLen)
    buffer := bytes.NewBufferString("")
    for _, chunk := range chunks {
        bytes, err := rsa.EncryptPKCS1v15(rand.Reader, r.publicKey, chunk)
        if err != nil {
            return "", err
        }
        buffer.Write(bytes)
    }
    return base64.RawURLEncoding.EncodeToString(buffer.Bytes()), nil
}
// 私钥解密
func (r *XRsa) PrivateDecrypt(encrypted string) (string, error) {
    partLen := r.publicKey.N.BitLen() / 8
    raw, err := base64.RawURLEncoding.DecodeString(encrypted)
    chunks := split([]byte(raw), partLen)
    buffer := bytes.NewBufferString("")
    for _, chunk := range chunks {
        decrypted, err := rsa.DecryptPKCS1v15(rand.Reader, r.privateKey, chunk)
        if err != nil {
            return "", err
        }
        buffer.Write(decrypted)
    }
    return buffer.String(), err
}
// 数据加签
func (r *XRsa) Sign(data string) (string, error) {
    h := RSA_ALGORITHM_SIGN.New()
    h.Write([]byte(data))
    hashed := h.Sum(nil)
    sign, err := rsa.SignPKCS1v15(rand.Reader, r.privateKey, RSA_ALGORITHM_SIGN, hashed)
    if err != nil {
        return "", err
    }
    return base64.RawURLEncoding.EncodeToString(sign), err
}
// 数据验签
func (r *XRsa) Verify(data string, sign string) error {
    h := RSA_ALGORITHM_SIGN.New()
    h.Write([]byte(data))
    hashed := h.Sum(nil)
    decodedSign, err := base64.RawURLEncoding.DecodeString(sign)
    if err != nil {
        return err
    }
    return rsa.VerifyPKCS1v15(r.publicKey, RSA_ALGORITHM_SIGN, hashed, decodedSign)
}
func MarshalPKCS8PrivateKey(key *rsa.PrivateKey) []byte {
    info := struct {
        Version             int
        PrivateKeyAlgorithm []asn1.ObjectIdentifier
        PrivateKey          []byte
    }{}
    info.Version = 0
    info.PrivateKeyAlgorithm = make([]asn1.ObjectIdentifier, 1)
    info.PrivateKeyAlgorithm[0] = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}
    info.PrivateKey = x509.MarshalPKCS1PrivateKey(key)
    k, _ := asn1.Marshal(info)
    return k
}
func split(buf []byte, lim int) [][]byte {
    var chunk []byte
    chunks := make([][]byte, 0, len(buf)/lim+1)
    for len(buf) >= lim {
        chunk, buf = buf[:lim], buf[lim:]
        chunks = append(chunks, chunk)
    }
    if len(buf) > 0 {
        chunks = append(chunks, buf[:len(buf)])
    }
    return chunks
}