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104 lines
3.1 KiB
Go
104 lines
3.1 KiB
Go
package envauth
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import (
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"crypto/pbkdf2"
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"crypto/sha256"
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"crypto/subtle"
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"errors"
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)
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var ErrUnauthorized = errors.New("unauthorized")
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type BasicAuthVerifier interface {
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Verify(string, string) error
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}
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// BasicCredentials holds user credentials
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type BasicCredentials struct {
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Username string `json:"username"`
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Password string `json:"password"`
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}
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// Returns true if username and password match.
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// Uses SHA-256 and constant-time techniques to avoid revealing whether the username or password matches through timing attacks.
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func (c BasicCredentials) Verify(username string, password string) error {
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if len(password) == 0 {
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return ErrUnauthorized
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}
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equal := 1
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// We hash rather than completely relying on subtle.ConstantTimeCompare([]byte(c.Username), []byte(username))
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// out of an abundance of caution since optimizations have caused similar methods to fail in other languages.
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// (we also use it because it gives back 1 rather than true, which we can use in the next step)
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knownUsernameHash := sha256.Sum256([]byte(c.Username))
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usernameHash := sha256.Sum256([]byte(username))
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v := subtle.ConstantTimeCompare(knownUsernameHash[:], usernameHash[:]) // 1 if same
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equal = subtle.ConstantTimeSelect(v, equal, 0) // v ? x : y
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knownPasswordHash := sha256.Sum256([]byte(c.Password))
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passwordHash := sha256.Sum256([]byte(password))
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v = subtle.ConstantTimeCompare(knownPasswordHash[:], passwordHash[:]) // 1 if same
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equal = subtle.ConstantTimeSelect(v, equal, 0) // v ? x : y
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if equal == 1 {
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return nil
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}
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return ErrUnauthorized
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}
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// PBKDF2Credentials holds user credentials
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type PBKDF2Credentials struct {
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Username string `json:"username"`
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DerivedKey []byte `json:"derived_key"`
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Salt []byte `json:"salt"` // should be at least 8 bytes
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Iterations int `json:"iterations"`
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}
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// Returns true if username and password match.
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// Uses PBKDF2 and constant-time techniques to avoid revealing whether the username or password matches through timing attacks.
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func (c PBKDF2Credentials) Verify(username string, password string) error {
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keyLen := len(c.DerivedKey)
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dkKnownUser, err := pbkdf2.Key(sha256.New, c.Username, c.Salt, c.Iterations, keyLen)
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if err != nil {
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return err
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}
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if len(password) == 0 {
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return ErrUnauthorized
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}
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dkUser, err := pbkdf2.Key(sha256.New, username, c.Salt, c.Iterations, keyLen)
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if err != nil {
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return err
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}
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dkPass, err := pbkdf2.Key(sha256.New, password, c.Salt, c.Iterations, keyLen)
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if err != nil {
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return err
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}
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equal := 1
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v := subtle.ConstantTimeCompare(dkUser, dkKnownUser) // 1 if same
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equal = subtle.ConstantTimeSelect(v, equal, 0) // v ? x : y
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v = subtle.ConstantTimeCompare(dkPass, c.DerivedKey) // 1 if same
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equal = subtle.ConstantTimeSelect(v, equal, 0) // v ? x : y
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if equal == 1 {
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return nil
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}
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return ErrUnauthorized
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}
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func (c PBKDF2Credentials) DeriveKey(username string, password string, keyLen int) ([]byte, error) {
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if keyLen == 0 {
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keyLen = len(c.DerivedKey)
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}
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return pbkdf2.Key(sha256.New, password, c.Salt, c.Iterations, keyLen)
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}
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var _ BasicAuthVerifier = (*BasicCredentials)(nil)
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var _ BasicAuthVerifier = (*PBKDF2Credentials)(nil)
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