Name

SSL_alert_type_string, SSL_alert_type_string_long
SSL_alert_desc_string, SSL_alert_desc_string_long

gets textual description of alert information

Library

libssl.lib

Synopsis

#include <openssl/ssl.h>

const char *SSL_alert_type_string(int value);
const char *SSL_alert_type_string_long(int value);

const char *SSL_alert_desc_string(int value);
const char *SSL_alert_desc_string_long(int value);

Detailed Description

SSL_alert_type_string() returns a one letter string indicating the type of the alert specified by value.

SSL_alert_type_string_long() returns a string indicating the type of the alert specified by value.

SSL_alert_desc_string() returns a two letter string as a short form describing the reason of the alert specified by value.

SSL_alert_desc_string_long() returns a string describing the reason of the alert specified by value.

When one side of an SSL/TLS communication wants to inform the peer about a special situation, it sends an alert. The alert is sent as a special message and does not influence the normal data stream (unless its contents results in the communication being canceled).

A warning alert is sent, when a non-fatal error condition occurs. The ``close notify'' alert is sent as a warning alert. Other examples for non-fatal errors are certificate errors (``certificate expired'', ``unsupported certificate''), for which a warning alert may be sent. (The sending party may however decide to send a fatal error.) The receiving side may cancel the connection on reception of a warning alert on it discretion.

Several alert messages must be sent as fatal alert messages as specified by the TLS RFC. A fatal alert always leads to a connection abort.

Return Values

The following strings can occur for SSL_alert_type_string() or SSL_alert_type_string_long():

``W''/``warning''
``F''/``fatal''
``U''/``unknown'': This indicates that no support is available for this alert type. Probably value does not contain a correct alert message.

The following strings can occur for SSL_alert_desc_string() or SSL_alert_desc_string_long():

``CN''/``close notify'': The connection shall be closed. This is a warning alert.

``UM''/``unexpected message'': An inappropriate message was received. This alert is always fatal and should never be observed in communication between proper implementations.

``BM''/``bad record mac'': This alert is returned if a record is received with an incorrect MAC. This message is always fatal.

``DF''/``decompression failure'': The decompression function received improper input (e.g. data that would expand to excessive length). This message is always fatal.

``HF''/``handshake failure'': Reception of a handshake_failure alert message indicates that the sender was unable to negotiate an acceptable set of security parameters given the options available. This is a fatal error.

``NC''/``no certificate'': A client, that was asked to send a certificate, does not send a certificate (SSLv3 only).

``BC''/``bad certificate'': A certificate was corrupt, contained signatures that did not verify correctly, etc

``UC''/``unsupported certificate'': A certificate was of an unsupported type.

``CR''/``certificate revoked'': A certificate was revoked by its signer.

``CE''/``certificate expired'': A certificate has expired or is not currently valid.

``CU''/``certificate unknown'': Some other (unspecified) issue arose in processing the certificate, rendering it unacceptable.

``IP''/``illegal parameter'': A field in the handshake was out of range or inconsistent with other fields. This is always fatal.

``DC''/``decryption failed'': A TLSCiphertext decrypted in an invalid way: either it wasn't an even multiple of the block length or its padding values, when checked, weren't correct. This message is always fatal.

``RO''/``record overflow'': A TLSCiphertext record was received which had a length more than 2^14+2048 bytes, or a record decrypted to a TLSCompressed record with more than 2^14+1024 bytes. This message is always fatal.

``CA''/``unknown CA'': A valid certificate chain or partial chain was received, but the certificate was not accepted because the CA certificate could not be located or couldn't be matched with a known, trusted CA. This message is always fatal.

``AD''/``access denied'': A valid certificate was received, but when access control was applied, the sender decided not to proceed with negotiation. This message is always fatal.

``DE''/``decode error'': A message could not be decoded because some field was out of the specified range or the length of the message was incorrect. This message is always fatal.

``CY''/``decrypt error'': A handshake cryptographic operation failed, including being unable to correctly verify a signature, decrypt a key exchange, or validate a finished message.

``ER''/``export restriction'': A negotiation not in compliance with export restrictions was detected; for example, attempting to transfer a 1024 bit ephemeral RSA key for the RSA_EXPORT handshake method. This message is always fatal.

``PV''/``protocol version'': The protocol version the client has attempted to negotiate is recognized, but not supported. (For example, old protocol versions might be avoided for security reasons). This message is always fatal.

``IS''/``insufficient security'': Returned instead of handshake_failure when a negotiation has failed specifically because the server requires ciphers more secure than those supported by the client. This message is always fatal.

``IE''/``internal error'': An internal error unrelated to the peer or the correctness of the protocol makes it impossible to continue (such as a memory allocation failure). This message is always fatal.

``US''/``user canceled'': This handshake is being canceled for some reason unrelated to a protocol failure. If the user cancels an operation after the handshake is complete, just closing the connection by sending a close_notify is more appropriate. This alert should be followed by a close_notify. This message is generally a warning.

``NR''/``no renegotiation'': Sent by the client in response to a hello request or by the server in response to a client hello after initial handshaking. Either of these would normally lead to renegotiation; when that is not appropriate, the recipient should respond with this alert; at that point, the original requester can decide whether to proceed with the connection. One case where this would be appropriate would be where a server has spawned a process to satisfy a request; the process might receive security parameters (key length, authentication, etc.) at startup and it might be difficult to communicate changes to these parameters after that point. This message is always a warning.

``UK''/``unknown'': This indicates that no description is available for this alert type. Probably value does not contain a correct alert message.

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