Ilia Denisov
62 lines
2.1 KiB
Go
62 lines
2.1 KiB
Go
package auth
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import (
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"crypto/rand"
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"errors"
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"fmt"
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"strings"
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"golang.org/x/crypto/bcrypt"
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)
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// CodeLength is the fixed length of the decimal code delivered by
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// SendEmailCode. The OpenAPI description ("six-digit") locks the value
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// at six; tests cannot lower it without breaking the contract test
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// against the schema.
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const CodeLength = 6
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// codeBcryptCost is the bcrypt cost used to store the hashed code in
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// auth_challenges.code_hash. Cost 10 matches the convention documented
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// for admin password storage in `backend/README.md` §12. Six-digit codes
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// have only ~1M entropy, so the bcrypt slowdown is what bounds online
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// attacks together with the per-challenge attempt ceiling.
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const codeBcryptCost = bcrypt.DefaultCost
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// generateCode returns a random CodeLength-character decimal string. The
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// modulo bias when mapping uniform bytes to ten digits is acceptable for
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// short-lived registration codes — the per-challenge attempt ceiling and
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// the TTL bound abuse far more tightly than the negligible bias.
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func generateCode() (string, error) {
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digits := make([]byte, CodeLength)
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if _, err := rand.Read(digits); err != nil {
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return "", fmt.Errorf("auth: generate code: %w", err)
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}
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var sb strings.Builder
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sb.Grow(CodeLength)
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for _, b := range digits {
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sb.WriteByte('0' + b%10)
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}
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return sb.String(), nil
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}
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// hashCode returns the bcrypt hash of code using the package-level cost.
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func hashCode(code string) ([]byte, error) {
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return bcrypt.GenerateFromPassword([]byte(code), codeBcryptCost)
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}
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// verifyCode reports whether code matches hash. The function is a thin
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// wrapper around bcrypt.CompareHashAndPassword so the comparison is
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// constant-time on the matching path. Returns nil on match,
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// ErrCodeMismatch when the bcrypt mismatch error fires, and a wrapped
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// error for any other failure (e.g. malformed hash).
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func verifyCode(hash []byte, code string) error {
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err := bcrypt.CompareHashAndPassword(hash, []byte(code))
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if err == nil {
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return nil
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}
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if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
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return ErrCodeMismatch
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}
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return fmt.Errorf("auth: verify code: %w", err)
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}
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