Implement EMV application selection

* emv_tal_select_app() is responsible for selecting the application,
  validating the FCI and ensuring that the AID and DF Name match, in
  accordance with EMV 4.4 Book 1, 12.4
* emv_select_application() is responsible updating the candidate
  application list and determining the outcome of the application
  selection attempt in accordance with EMV 4.4 Book 4, 11.3

src/emv.c

@@ -29,6 +29,10 @@
 #define EMV_DEBUG_SOURCE EMV_DEBUG_SOURCE_EMV
 #include "emv_debug.h"
 
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
 const char* emv_lib_version_string(void)
 {
 	return EMV_UTILS_VERSION_STRING;
@@ -51,6 +55,7 @@ const char* emv_outcome_get_string(enum emv_outcome_t outcome)
 		case EMV_OUTCOME_CARD_ERROR: return "Card error"; // Message 06
 		case EMV_OUTCOME_CARD_BLOCKED: return "Card blocked"; // Not in EMV specification
 		case EMV_OUTCOME_NOT_ACCEPTED: return "Not accepted"; // Message 0C
+		case EMV_OUTCOME_TRY_AGAIN: return "Try again"; // Message 13
 	}
 
 	return "Invalid outcome";
@@ -346,3 +351,83 @@ int emv_build_candidate_list(
 
 	return 0;
 }
+
+int emv_select_application(
+	struct emv_ttl_t* ttl,
+	struct emv_app_list_t* app_list,
+	unsigned int index,
+	struct emv_app_t** selected_app
+)
+{
+	int r;
+	struct emv_app_t* current_app = NULL;
+	uint8_t current_aid[16];
+	size_t current_aid_len;
+
+	if (!ttl || !app_list || !selected_app) {
+		emv_debug_trace_msg("ttl=%p, app_list=%p, index=%u, selected_app=%p", ttl, app_list, index, selected_app);
+		emv_debug_error("Invalid parameter");
+		return EMV_ERROR_INVALID_PARAMETER;
+	}
+	*selected_app = NULL;
+
+	current_app = emv_app_list_remove_index(app_list, index);
+	if (!current_app) {
+		return EMV_ERROR_INVALID_PARAMETER;
+	}
+
+	if (current_app->aid->length > sizeof(current_aid)) {
+		goto try_again;
+	}
+	current_aid_len = current_app->aid->length;
+	memcpy(current_aid, current_app->aid->value, current_app->aid->length);
+	emv_app_free(current_app);
+	current_app = NULL;
+
+	r = emv_tal_select_app(
+		ttl,
+		current_aid,
+		current_aid_len,
+		selected_app
+	);
+	if (r) {
+		emv_debug_trace_msg("emv_tal_select_app() failed; r=%d", r);
+		if (r < 0) {
+			emv_debug_error("Error during application selection; terminate session");
+			if (r == EMV_TAL_ERROR_CARD_BLOCKED) {
+				r = EMV_OUTCOME_CARD_BLOCKED;
+			} else {
+				r = EMV_OUTCOME_CARD_ERROR;
+			}
+			goto exit;
+		}
+		if (r > 0) {
+			emv_debug_info("Failed to select application; continue session");
+			goto try_again;
+		}
+	}
+
+	// Success
+	r = 0;
+	goto exit;
+
+try_again:
+	// If no applications remain, terminate session
+	// Otherwise, try again
+	// See EMV 4.4 Book 1, 12.4
+	// See EMV 4.4 Book 4, 11.3
+	if (emv_app_list_is_empty(app_list)) {
+		emv_debug_info("Candidate list empty");
+		r = EMV_OUTCOME_NOT_ACCEPTED;
+	} else {
+		r = EMV_OUTCOME_TRY_AGAIN;
+	}
+
+exit:
+	if (current_app) {
+		emv_app_free(current_app);
+		current_app = NULL;
+	}
+
+	return r;
+}

src/emv.h

@@ -31,6 +31,7 @@ __BEGIN_DECLS
 struct emv_ttl_t;
 struct emv_tlv_list_t;
 struct emv_app_list_t;
+struct emv_app_t;
 
 /**
  * EMV errors
@@ -51,6 +52,7 @@ enum emv_outcome_t {
 	EMV_OUTCOME_CARD_ERROR = 1, ///< Malfunction of the card or non-conformance to Answer To Reset (ATR)
 	EMV_OUTCOME_CARD_BLOCKED = 2, ///< Card blocked
 	EMV_OUTCOME_NOT_ACCEPTED = 3, ///< Card not accepted or no supported applications
+	EMV_OUTCOME_TRY_AGAIN = 4, ///< Try again by selecting a different application
 };
 
 /**
@@ -110,6 +112,32 @@ int emv_build_candidate_list(
 	struct emv_app_list_t* app_list
 );
 
+/**
+ * Select EMV application by index from the candidate application list. The
+ * candidate application list will be updated by removing the selected
+ * application regardless of processing outcome. If application selection fails
+ * this function will return either @ref EMV_OUTCOME_NOT_ACCEPTED or
+ * @ref EMV_OUTCOME_TRY_AGAIN, depending on whether the candidate application
+ * list is empty or not.
+ * @remark See EMV 4.4 Book 1, 12.4
+ * @remark See EMV 4.4 Book 4, 11.3
+ *
+ * @param ttl EMV Terminal Transport Layer context
+ * @param app_list Candidate application list
+ * @param index Index (starting from zero) of EMV application to select
+ * @param selected_app Selected EMV application output. Use @ref emv_app_free() to free memory.
+ *
+ * @return Zero for success
+ * @return Less than zero for errors. See @ref emv_error_t
+ * @return Greater than zero for EMV processing outcome. See @ref emv_outcome_t
+ */
+int emv_select_application(
+	struct emv_ttl_t* ttl,
+	struct emv_app_list_t* app_list,
+	unsigned int index,
+	struct emv_app_t** selected_app
+);
+
 __END_DECLS
 
 #endif

src/emv_tal.c

@@ -437,6 +437,94 @@ int emv_tal_find_supported_apps(
 	return 0;
 }
 
+int emv_tal_select_app(
+	struct emv_ttl_t* ttl,
+	const uint8_t* aid,
+	size_t aid_len,
+	struct emv_app_t** selected_app
+)
+{
+	int r;
+	uint8_t fci[EMV_RAPDU_DATA_MAX];
+	size_t fci_len = sizeof(fci);
+	uint16_t sw1sw2;
+	struct emv_app_t* app;
+
+	if (!ttl || !aid || aid_len < 5 || aid_len > 16 || !selected_app) {
+		// Invalid parameters; terminate session
+		return EMV_TAL_ERROR_INVALID_PARAMETER;
+	}
+	*selected_app = NULL;
+
+	// SELECT application
+	// See EMV 4.4 Book 1, 12.4
+	emv_debug_info_data("SELECT application", aid, aid_len);
+	r = emv_ttl_select_by_df_name(ttl, aid, aid_len, fci, &fci_len, &sw1sw2);
+	if (r) {
+		emv_debug_trace_msg("emv_ttl_select_by_df_name() failed; r=%d", r);
+
+		// TTL failure; terminate session
+		// (bad card or reader)
+		emv_debug_error("TTL failure");
+		return EMV_TAL_ERROR_TTL_FAILURE;
+	}
+
+	if (sw1sw2 != 0x9000) {
+		switch (sw1sw2) {
+			case 0x6A81:
+				// Card blocked or SELECT not supported; terminate session
+				emv_debug_error("Card blocked or SELECT not supported");
+				return EMV_TAL_ERROR_CARD_BLOCKED;
+
+			case 0x6A82:
+				// Application not found; ignore app and continue
+				emv_debug_info("Application not found");
+				return EMV_TAL_RESULT_APP_NOT_FOUND;
+
+			case 0x6283:
+				// Application blocked; ignore app and continue
+				emv_debug_info("Application is blocked");
+				return EMV_TAL_RESULT_APP_BLOCKED;
+
+			default:
+				// Unknown error; ignore app and continue
+				// See EMV Book 1, 12.4, regarding status other than 9000
+				emv_debug_error("SW1SW2=0x%04hX\n", sw1sw2);
+				return EMV_TAL_RESULT_APP_SELECTION_FAILED;
+		}
+	}
+
+	emv_debug_info_tlv("FCI", fci, fci_len);
+
+	// Parse FCI to confirm that selected application is valid
+	app = emv_app_create_from_fci(fci, fci_len);
+	if (!app) {
+		emv_debug_trace_msg("emv_app_create_from_fci() failed; app=%p", app);
+
+		// Failed to parse FCI; ignore app and continue
+		// See EMV Book 1, 12.4, regarding format errors
+		emv_debug_error("Failed to parse application FCI");
+		return EMV_TAL_RESULT_APP_FCI_PARSE_FAILED;
+	}
+
+	// Ensure that the AID used by the SELECT command exactly matches the
+	// DF Name (field 84) provided by the FCI
+	// See EMV 4.4 Book 1, 12.4
+	// NOTE: emv_app_create_from_fci() sets AID to DF Name (field 84)
+	if (app->aid->length != aid_len ||
+		memcmp(app->aid->value, aid, aid_len)
+	) {
+		emv_debug_error("DF Name mismatch");
+		emv_app_free(app);
+		return EMV_TAL_RESULT_APP_SELECTION_FAILED;
+	}
+
+	// Output
+	*selected_app = app;
+
+	return 0;
+}
+
 int emv_tal_parse_gpo_response(
 	const void* buf,
 	size_t len,

src/emv_tal.h

@@ -24,12 +24,14 @@
 
 #include <sys/cdefs.h>
 #include <stddef.h>
+#include <stdint.h>
 
 __BEGIN_DECLS
 
 // Forward declarations
 struct emv_ttl_t;
 struct emv_app_list_t;
+struct emv_app_t;
 struct emv_tlv_list_t;
 struct emv_tlv_t;
 
@@ -59,6 +61,10 @@ enum emv_tal_result_t {
 	EMV_TAL_RESULT_PSE_SFI_NOT_FOUND, ///< Failed to find Short File Identifier (SFI) for Payment System Environment (PSE)
 	EMV_TAL_RESULT_PSE_AEF_PARSE_FAILED, ///< Failed to parse Application Elementary File (AEF) of Payment System Environment (PSE)
 	EMV_TAL_RESULT_PSE_AEF_INVALID, ///< Invalid Payment System Environment (PSE) Application Elementary File (AEF) record
+	EMV_TAL_RESULT_APP_NOT_FOUND, ///< Selected application not found
+	EMV_TAL_RESULT_APP_BLOCKED, ///< Selected application is blocked
+	EMV_TAL_RESULT_APP_SELECTION_FAILED, ///< Application selection failed
+	EMV_TAL_RESULT_APP_FCI_PARSE_FAILED, ///< Failed to parse File Control Information (FCI) for selected application
 };
 
 /**
@@ -102,6 +108,30 @@ int emv_tal_find_supported_apps(
 	struct emv_app_list_t* app_list
 );
 
+/**
+ * SELECT application and validate File Control Information (FCI)
+ * @remark See EMV 4.4 Book 1, 12.4
+ *
+ * @param ttl EMV Terminal Transport Layer context
+ * @param aid Application Identifier (AID) field. Must be 5 to 16 bytes.
+ * @param aid_len Length of Application Identifier (AID) field. Must be 5 to 16 bytes.
+ * @param selected_app Selected EMV application output. Use @ref emv_app_free() to free memory.
+ *
+ * @return Zero for success
+ * @return Less than zero indicates that the terminal should terminate the
+ *         card session. See @ref emv_tal_error_t
+ * @return Greater than zero indicates that selection or validation of the
+ *         application failed and that the terminal may continue the card
+ *         session. Typically the candidate application list should be
+ *         consulted next for remaining application options.
+ */
+int emv_tal_select_app(
+	struct emv_ttl_t* ttl,
+	const uint8_t* aid,
+	size_t aid_len,
+	struct emv_app_t** selected_app
+);
+
 /**
  * Parse GET PROCESSING OPTIONS response
  * @param buf Buffer containing GET PROCESSING OPTIONS response data