diff --git a/backend/submission.go b/backend/submission.go
index e54d09f7..bca14a2e 100644
--- a/backend/submission.go
+++ b/backend/submission.go
@@ -37,7 +37,13 @@ func treatSubmission(pathname string, team_id string, exercice_id string) {
 			cnt += scanner.Text()
 		}
 
-
-		log.Println(id, team, exercice, cnt)
+		if solved, err := exercice.CheckResponse(cnt, team); err != nil {
+			log.Println(id, "[ERR]", err)
+		} else if solved {
+			exercice.Solved(team)
+			log.Printf("%s Team %d SOLVED exercice %d\n", id, team.Id, exercice.Id)
+		} else {
+			log.Printf("%s Team %d submit an invalid solution for exercice %d\n", id, team.Id, exercice.Id)
+		}
 	}
 }
diff --git a/libfic/exercice.go b/libfic/exercice.go
index 1f96a863..8b00f4a5 100644
--- a/libfic/exercice.go
+++ b/libfic/exercice.go
@@ -1,6 +1,7 @@
 package fic
 
 import (
+	"errors"
 	"time"
 )
 
@@ -109,3 +110,27 @@ func (e Exercice) Solved(t Team) error {
 		return nil
 	}
 }
+
+func (e Exercice) CheckResponse(response string, t Team) (bool, error) {
+	if t.HasSolved(e) {
+		return true, nil
+	}
+
+	if err := e.NewTry(t); err != nil {
+		return false, err
+	} else if keys, err := e.GetKeys(); err != nil {
+		return false, err
+	} else {
+		if len(keys) < 1 {
+			return true, errors.New("Exercice with no key registered")
+		}
+
+		for _, k := range keys {
+			if !k.Check(response) {
+				return false, nil
+			}
+		}
+
+		return true, nil
+	}
+}
diff --git a/libfic/key.go b/libfic/key.go
index c570f236..e661b488 100644
--- a/libfic/key.go
+++ b/libfic/key.go
@@ -34,8 +34,12 @@ func (e Exercice) GetKeys() ([]Key, error) {
 	}
 }
 
+func getHashedKey(raw_value string) [64]byte {
+	return sha512.Sum512([]byte(raw_value))
+}
+
 func (e Exercice) AddRawKey(name string, raw_value string) (Key, error) {
-	return e.AddKey(name, sha512.Sum512([]byte(raw_value)))
+	return e.AddKey(name, getHashedKey(raw_value))
 }
 
 func (e Exercice) AddKey(name string, value [64]byte) (Key, error) {
@@ -67,3 +71,7 @@ func (k Key) Delete() (int64, error) {
 		return nb, err
 	}
 }
+
+func (k Key) Check(val string) bool {
+	return k.Value == getHashedKey(val)
+}
diff --git a/libfic/team.go b/libfic/team.go
index 57302509..e6507adb 100644
--- a/libfic/team.go
+++ b/libfic/team.go
@@ -67,3 +67,12 @@ func (t Team) Delete() (int64, error) {
 		return nb, err
 	}
 }
+
+func (t Team) HasSolved(e Exercice) bool {
+	var nb int
+	if err := DBQueryRow("SELECT COUNT(id_exercice) FROM exercice_solved WHERE id_team = ? AND id_exercice = ?", t.Id, e.Id).Scan(&nb); err != nil {
+		return false
+	} else {
+		return nb > 0
+	}
+}