diff --git a/internal/pow/types.go b/internal/pow/types.go
new file mode 100644
index 0000000..b55b370
--- /dev/null
+++ b/internal/pow/types.go
@@ -0,0 +1,53 @@
+package pow
+
+import (
+	"errors"
+	"time"
+)
+
+// PoW package specific errors
+var (
+	ErrInvalidHMAC      = errors.New("challenge HMAC signature is invalid")
+	ErrExpiredChallenge = errors.New("challenge has expired")
+	ErrInvalidSolution  = errors.New("proof of work solution is invalid")
+	ErrInvalidDifficulty = errors.New("difficulty level is invalid")
+	ErrMalformedChallenge = errors.New("challenge format is malformed")
+)
+
+// Challenge represents a Proof of Work challenge with HMAC authentication
+type Challenge struct {
+	Timestamp  int64  `json:"timestamp"`
+	Difficulty int    `json:"difficulty"`
+	Resource   string `json:"resource"`
+	Random     string `json:"random"`
+	HMAC       string `json:"hmac"`
+}
+
+// Solution represents a client's solution to a PoW challenge
+type Solution struct {
+	Challenge Challenge `json:"challenge"`
+	Nonce     string    `json:"nonce"`
+}
+
+// ChallengeRequest represents a request for a new challenge
+type ChallengeRequest struct{}
+
+// SolutionRequest represents a client's submission of a solved challenge
+type SolutionRequest struct {
+	Challenge Challenge `json:"challenge"`
+	Nonce     string    `json:"nonce"`
+}
+
+// Config holds configuration for the PoW system
+type Config struct {
+	DefaultDifficulty     int           // Default difficulty in bits (e.g., 4)
+	MaxDifficulty         int           // Maximum allowed difficulty (e.g., 10)
+	MinDifficulty         int           // Minimum allowed difficulty (e.g., 3)
+	ChallengeTTL          time.Duration // Time-to-live for challenges (e.g., 5 minutes)
+	HMACSecret            []byte        // Secret key for HMAC signing
+	Resource              string        // Resource identifier (e.g., "quotes")
+	LoadAdjustmentBits    int           // Extra difficulty bits when server under load
+	FailurePenaltyBits    int           // Extra difficulty bits per failure group
+	MaxFailurePenaltyBits int           // Maximum failure penalty bits
+}
+