90 lines
1.8 KiB
Go
90 lines
1.8 KiB
Go
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package totpext
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import (
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"crypto/hmac"
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"crypto/rand"
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"crypto/sha1"
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"encoding/base32"
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"encoding/binary"
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"fmt"
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"hash"
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"net/url"
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"strconv"
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"time"
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)
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// https://datatracker.ietf.org/doc/html/rfc6238
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// https://datatracker.ietf.org/doc/html/rfc4226
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// https://datatracker.ietf.org/doc/html/rfc2104
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// https://en.wikipedia.org/wiki/Universal_2nd_Factor
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// https://en.wikipedia.org/wiki/HMAC-based_one-time_password
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// https://en.wikipedia.org/wiki/HMAC
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func TOTP(key []byte) string {
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t := time.Now().Unix() / 30
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return generateTOTP(sha1.New, key, t, 6)
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}
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func Validate(key []byte, totp string) bool {
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t := time.Now().Unix() / 30
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if generateTOTP(sha1.New, key, t, 6) == totp {
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return true
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}
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if generateTOTP(sha1.New, key, t-1, 6) == totp {
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return true
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}
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if generateTOTP(sha1.New, key, t+1, 6) == totp {
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return true
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}
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return false
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}
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func GenerateSecret() ([]byte, error) {
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secret := make([]byte, 20)
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_, err := rand.Read(secret)
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if err != nil {
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return nil, err
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}
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return secret, nil
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}
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func generateTOTP(algo func() hash.Hash, secret []byte, time int64, returnDigits int) string {
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msg := make([]byte, 8)
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binary.BigEndian.PutUint64(msg, uint64(time))
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mac := hmac.New(algo, secret)
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mac.Write(msg)
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hmacResult := mac.Sum(nil)
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offsetBits := hmacResult[len(hmacResult)-1] & 0x0F
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p := hmacResult[offsetBits : offsetBits+4]
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truncated := binary.BigEndian.Uint32(p) & 0x7FFFFFFF // Last 31 bits
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val := strconv.Itoa(int(truncated))
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for len(val) < returnDigits {
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val = "0" + val
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}
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val = val[len(val)-returnDigits:]
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return val
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}
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func GenerateOTPAuth(ccn string, key []byte, accountmail string, issuer string) string {
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return fmt.Sprintf("otpauth://totp/%v:%v?secret=%v&issuer=%v&algorithm=%v&period=%v&digits=%v",
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ccn,
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url.QueryEscape(accountmail),
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base32.StdEncoding.EncodeToString(key),
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issuer,
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"SHA1",
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"30",
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"6")
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}
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