diff --git a/libsks/src/pkcs11_api.c b/libsks/src/pkcs11_api.c
index 370264aa..3a0b6ff7 100644
--- a/libsks/src/pkcs11_api.c
+++ b/libsks/src/pkcs11_api.c
@@ -25,6 +25,13 @@ static int inited;
 			return CKR_ARGUMENTS_BAD; \
 	} while (0)
 
+#define SANITY_SESSION_FLAGS(flags) \
+	do { \
+		if (flags & ~(CKF_RW_SESSION | \
+			      CKF_SERIAL_SESSION)) \
+			return CKR_ARGUMENTS_BAD; \
+	} while (0)
+
 #define REGISTER_CK_FUNCTION(_function)		._function = _function
 #define DO_NOT_REGISTER_CK_FUNCTION(_function)	._function = NULL
 
@@ -41,10 +48,10 @@ static const CK_FUNCTION_LIST libsks_function_list = {
 	REGISTER_CK_FUNCTION(C_InitToken),
 	DO_NOT_REGISTER_CK_FUNCTION(C_InitPIN),
 	DO_NOT_REGISTER_CK_FUNCTION(C_SetPIN),
-	DO_NOT_REGISTER_CK_FUNCTION(C_OpenSession),
-	DO_NOT_REGISTER_CK_FUNCTION(C_CloseSession),
-	DO_NOT_REGISTER_CK_FUNCTION(C_CloseAllSessions),
-	DO_NOT_REGISTER_CK_FUNCTION(C_GetSessionInfo),
+	REGISTER_CK_FUNCTION(C_OpenSession),
+	REGISTER_CK_FUNCTION(C_CloseSession),
+	REGISTER_CK_FUNCTION(C_CloseAllSessions),
+	REGISTER_CK_FUNCTION(C_GetSessionInfo),
 	DO_NOT_REGISTER_CK_FUNCTION(C_GetOperationState),
 	DO_NOT_REGISTER_CK_FUNCTION(C_SetOperationState),
 	DO_NOT_REGISTER_CK_FUNCTION(C_Login),
@@ -342,41 +349,103 @@ CK_RV C_OpenSession(CK_SLOT_ID slot,
 		    CK_NOTIFY callback,
 		    CK_SESSION_HANDLE_PTR session)
 {
-	(void)slot;
-	(void)flags;
-	(void)cookie;
-	(void)callback;
-	(void)session;
+	CK_RV rv;
+
 	SANITY_LIB_INIT;
+	SANITY_SESSION_FLAGS(flags);
 
-	return CKR_FUNCTION_NOT_SUPPORTED;
+	/* Specific mandated flag */
+	if (!(flags & CKF_SERIAL_SESSION))
+		return CKR_SESSION_PARALLEL_NOT_SUPPORTED;
 
+	rv = sks_ck_open_session(slot, flags, cookie, callback, session);
+
+	switch (rv) {
+	case CKR_CRYPTOKI_NOT_INITIALIZED:
+	case CKR_DEVICE_ERROR:
+	case CKR_DEVICE_MEMORY:
+	case CKR_DEVICE_REMOVED:
+	case CKR_FUNCTION_FAILED:
+	case CKR_GENERAL_ERROR:
+	case CKR_HOST_MEMORY:
+	case CKR_OK:
+	case CKR_SESSION_COUNT:
+	case CKR_SESSION_PARALLEL_NOT_SUPPORTED:
+	case CKR_SESSION_READ_WRITE_SO_EXISTS:
+	case CKR_SLOT_ID_INVALID:
+	case CKR_TOKEN_NOT_PRESENT:
+	case CKR_TOKEN_NOT_RECOGNIZED:
+	case CKR_TOKEN_WRITE_PROTECTED:
+	case CKR_ARGUMENTS_BAD:
+		break;
+	default:
+		ASSERT(rv);
+	}
+
+	return rv;
 }
 
 CK_RV C_CloseSession(CK_SESSION_HANDLE session)
 {
-	(void)session;
+	CK_RV rv;
+
 	SANITY_LIB_INIT;
 
-	return CKR_FUNCTION_NOT_SUPPORTED;
+	rv = sks_ck_close_session(session);
+
+	switch (rv) {
+	case CKR_CRYPTOKI_NOT_INITIALIZED:
+	case CKR_DEVICE_ERROR:
+	case CKR_DEVICE_MEMORY:
+	case CKR_DEVICE_REMOVED:
+	case CKR_FUNCTION_FAILED:
+	case CKR_GENERAL_ERROR:
+	case CKR_HOST_MEMORY:
+	case CKR_OK:
+	case CKR_SESSION_CLOSED:
+	case CKR_SESSION_HANDLE_INVALID:
+		break;
+	default:
+		ASSERT(rv);
+	}
+
+	return rv;
 }
 
 CK_RV C_CloseAllSessions(CK_SLOT_ID slot)
 {
-	(void)slot;
+	CK_RV rv;
+
 	SANITY_LIB_INIT;
 
-	return CKR_FUNCTION_NOT_SUPPORTED;
+	rv = sks_ck_close_all_sessions(slot);
+
+	switch (rv) {
+	case CKR_CRYPTOKI_NOT_INITIALIZED:
+	case CKR_DEVICE_ERROR:
+	case CKR_DEVICE_MEMORY:
+	case CKR_DEVICE_REMOVED:
+	case CKR_FUNCTION_FAILED:
+	case CKR_GENERAL_ERROR:
+	case CKR_HOST_MEMORY:
+	case CKR_OK:
+	case CKR_SLOT_ID_INVALID:
+	case CKR_TOKEN_NOT_PRESENT:
+		break;
+	default:
+		ASSERT(rv);
+	}
+
+	return rv;
 }
 
 CK_RV C_GetSessionInfo(CK_SESSION_HANDLE session,
 		       CK_SESSION_INFO_PTR info)
 {
-	(void)session;
-	(void)info;
 	SANITY_LIB_INIT;
+	SANITY_NONNULL_PTR(info);
 
-	return CKR_FUNCTION_NOT_SUPPORTED;
+	return sks_ck_get_session_info(session, info);
 }
 
 CK_RV C_InitPIN(CK_SESSION_HANDLE session,
diff --git a/libsks/src/pkcs11_token.c b/libsks/src/pkcs11_token.c
index fccfbbaf..98b9f426 100644
--- a/libsks/src/pkcs11_token.c
+++ b/libsks/src/pkcs11_token.c
@@ -253,3 +253,70 @@ CK_RV sks_ck_token_mechanism_info(CK_SLOT_ID slot,
 	}
 	return rv;
 }
+
+/*
+ * TODO: with following code, the session identifier are abstracted by the SKS
+ * library. It could be better to let the TA provide the handle, so that
+ * several applications can see the same session identifiers.
+ */
+CK_RV sks_ck_open_session(CK_SLOT_ID slot,
+		          CK_FLAGS flags,
+		          CK_VOID_PTR cookie,
+		          CK_NOTIFY callback,
+		          CK_SESSION_HANDLE_PTR session)
+{
+	uint32_t ctrl[1] = { slot };
+	unsigned long cmd;
+	uint32_t handle;
+	size_t out_sz = sizeof(handle);
+	CK_RV rv;
+
+	if (cookie || callback) {
+		LOG_ERROR("C_OpenSession does not handle callback yet\n");
+		return CKR_FUNCTION_NOT_SUPPORTED;
+	}
+
+	if (flags & CKF_RW_SESSION)
+		cmd = SKS_CMD_CK_OPEN_RW_SESSION;
+	else
+		cmd = SKS_CMD_CK_OPEN_RO_SESSION;
+
+	rv = ck_invoke_ta(NULL, cmd, &ctrl, sizeof(ctrl),
+			  NULL, 0, &handle, &out_sz);
+	if (rv)
+		return rv;
+
+	*session = handle;
+
+	return CKR_OK;
+}
+
+CK_RV sks_ck_close_session(CK_SESSION_HANDLE session)
+{
+	uint32_t ctrl[1] = { (uint32_t)session };
+
+	return ck_invoke_ta(NULL, SKS_CMD_CK_CLOSE_SESSION,
+			    &ctrl, sizeof(ctrl), NULL, 0, NULL, NULL);
+}
+
+/*
+ * Scan all registered session handle by the lib
+ * and close all session related to the target slot.
+ */
+CK_RV sks_ck_close_all_sessions(CK_SLOT_ID slot)
+{
+	uint32_t ctrl[1] = { (uint32_t)slot };
+
+	return ck_invoke_ta(NULL, SKS_CMD_CK_CLOSE_ALL_SESSIONS,
+			    &ctrl, sizeof(ctrl), NULL, 0, NULL, NULL);
+}
+
+CK_RV sks_ck_get_session_info(CK_SESSION_HANDLE session,
+			      CK_SESSION_INFO_PTR info)
+{
+	uint32_t ctrl[1] = { (uint32_t)session };
+	size_t info_size = sizeof(CK_SESSION_INFO);
+
+	return ck_invoke_ta(NULL, SKS_CMD_CK_SESSION_INFO,
+			    &ctrl, sizeof(ctrl), NULL, 0, info, &info_size);
+}
diff --git a/libsks/src/pkcs11_token.h b/libsks/src/pkcs11_token.h
index affdee4a..d52ab9ef 100644
--- a/libsks/src/pkcs11_token.h
+++ b/libsks/src/pkcs11_token.h
@@ -30,4 +30,14 @@ CK_RV sks_ck_init_token(CK_SLOT_ID slot,
 			CK_ULONG pin_len,
 			CK_UTF8CHAR_PTR label);
 
+CK_RV sks_ck_open_session(CK_SLOT_ID slot,
+		          CK_FLAGS flags,
+		          CK_VOID_PTR cookie,
+		          CK_NOTIFY callback,
+		          CK_SESSION_HANDLE_PTR session);
+CK_RV sks_ck_close_session(CK_SESSION_HANDLE session);
+CK_RV sks_ck_close_all_sessions(CK_SLOT_ID slot);
+CK_RV sks_ck_get_session_info(CK_SESSION_HANDLE session,
+			      CK_SESSION_INFO_PTR info);
+
 #endif /*__PKCS11_TOKEN_H*/