error_t pemReadDhParameters(const char_t *input, size_t length, DhParameters *params)
{
error_t error;
size_t i;
size_t j;
int_t k;
char_t *buffer;
const uint8_t *data;
Asn1Tag tag;
//Check parameters
if(input == NULL && length != 0)
return ERROR_INVALID_PARAMETER;
if(params == NULL)
return ERROR_INVALID_PARAMETER;
//Search for the beginning tag
k = pemSearchTag(input, length, "-----BEGIN DH PARAMETERS-----", 29);
//Failed to find the specified tag?
if(k < 0) return ERROR_INVALID_SYNTAX;
//Advance the pointer over the tag
input += k + 29;
length -= k + 29;
//Search for the end tag
k = pemSearchTag(input, length, "-----END DH PARAMETERS-----", 27);
//Invalid PEM file?
if(k <= 0) return ERROR_INVALID_SYNTAX;
//Length of the PEM structure
length = k;
//Allocate a memory buffer to hold the decoded data
buffer = osMemAlloc(length);
//Failed to allocate memory?
if(!buffer) return ERROR_OUT_OF_MEMORY;
//Copy the contents of the PEM structure
memcpy(buffer, input, length);
//Remove carriage returns and line feeds
for(i = 0, j = 0; i < length; i++)
{
if(buffer[i] != '\r' && buffer[i] != '\n')
buffer[j++] = buffer[i];
}
//Start of exception handling block
do
{
//The PEM file is Base64 encoded...
error = base64Decode(buffer, j, buffer, &length);
//Failed to decode the file?
if(error) break;
//Point to the resulting ASN.1 structure
data = (uint8_t *) buffer;
//Display ASN.1 structure
error = asn1DumpObject(data, length, 0);
//Any error to report?
if(error) break;
//The Diffie-Hellman parameters are encapsulated within a sequence
error = asn1ReadTag(data, length, &tag);
//Failed to decode ASN.1 tag?
if(error) break;
//Enforce encoding, type and class
error = asn1CheckTag(&tag, TRUE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_SEQUENCE);
//The tag does not match the criteria?
if(error) break;
//Point to the first field of the sequence
data = tag.value;
length = tag.length;
//Read the prime modulus
error = asn1ReadTag(data, length, &tag);
//Failed to decode ASN.1 tag?
if(error) break;
//Enforce encoding, type and class
error = asn1CheckTag(&tag, FALSE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_INTEGER);
//The tag does not match the criteria?
if(error) break;
//Convert the prime modulus to a multiple precision integer
error = mpiReadRaw(¶ms->p, tag.value, tag.length);
//Any error to report?
if(error) break;
//Point to the next field
data += tag.totalLength;
length -= tag.totalLength;
//Read the generator
error = asn1ReadTag(data, length, &tag);
//Failed to decode ASN.1 tag?
if(error) break;
//Enforce encoding, type and class
error = asn1CheckTag(&tag, FALSE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_INTEGER);
//The tag does not match the criteria?
if(error) break;
//Convert the generator to a multiple precision integer
error = mpiReadRaw(¶ms->g, tag.value, tag.length);
//Any error to report?
if(error) break;
//Debug message
TRACE_DEBUG("Diffie-Hellman parameters:\r\n");
TRACE_DEBUG(" Prime modulus:\r\n");
TRACE_DEBUG_MPI(" ", ¶ms->p);
TRACE_DEBUG(" Generator:\r\n");
TRACE_DEBUG_MPI(" ", ¶ms->g);
//End of exception handling block
} while(0);
//Release previously allocated memory
osMemFree(buffer);
//Clean up side effects if necessary
if(error)
dhFreeParameters(params);
//Return status code
return error;
}
error_t snmpParseMessage(SnmpAgentContext *context, const uint8_t *p, size_t length)
{
error_t error;
int32_t version;
Asn1Tag tag;
//Debug message
TRACE_INFO("SNMP message received from %s port %" PRIu16 " (%" PRIuSIZE " bytes)...\r\n",
ipAddrToString(&context->remoteIpAddr, NULL), context->remotePort, length);
//Display the contents of the SNMP message
TRACE_DEBUG_ARRAY(" ", p, length);
//Dump ASN.1 structure
error = asn1DumpObject(p, length, 0);
//Any error to report?
if(error) return error;
//The SNMP message is encapsulated within a sequence
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Enforce encoding, class and type
error = asn1CheckTag(&tag, TRUE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_SEQUENCE);
//The tag does not match the criteria?
if(error) return error;
//Point to the first field of the sequence
p = tag.value;
length = tag.length;
//Read version identifier
error = asn1ReadInt32(p, length, &tag, &version);
//Failed to decode ASN.1 tag?
if(error) return error;
//The SNMP agent verifies the version number. If there is a mismatch,
//it discards the datagram and performs no further actions
if(version != context->version)
return ERROR_INVALID_VERSION;
//Point to the next field
p += tag.totalLength;
length -= tag.totalLength;
//Read SNMP community name
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Enforce encoding, class and type
error = asn1CheckTag(&tag, FALSE, ASN1_CLASS_UNIVERSAL, ASN1_TYPE_OCTET_STRING);
//The tag does not match the criteria?
if(error) return error;
//Save community name
context->request.community = tag.value;
context->request.communityLen = tag.length;
//Point to the next field
p += tag.totalLength;
length -= tag.totalLength;
//Read PDU
error = asn1ReadTag(p, length, &tag);
//Failed to decode ASN.1 tag?
if(error) return error;
//Check encoding
if(tag.constructed != TRUE)
return ERROR_WRONG_ENCODING;
//Enforce class
if(tag.class != ASN1_CLASS_CONTEXT_SPECIFIC)
return ERROR_INVALID_CLASS;
//Save PDU type
context->request.pduType = (SnmpPduType) tag.type;
//Process the protocol data unit
switch(context->request.pduType)
{
case SNMP_PDU_GET_REQUEST:
case SNMP_PDU_GET_NEXT_REQUEST:
//Parse GetRequest-PDU or GetNextRequest-PDU
error = snmpParseGetRequestPdu(context, tag.value, tag.length);
break;
case SNMP_PDU_GET_BULK_REQUEST:
//Parse GetBulkRequest-PDU
error = snmpParseGetBulkRequestPdu(context, tag.value, tag.length);
break;
case SNMP_PDU_SET_REQUEST:
//Parse SetRequest-PDU
error = snmpParseSetRequestPdu(context, tag.value, tag.length);
break;
default:
//Invalid PDU type
error = ERROR_INVALID_TYPE;
break;
}
//Failed to parse PDU?
if(error)
return error;
//Format response PDU header
error = snmpWritePduHeader(context);
//Any error to report?
if(error) return error;
//Debug message
TRACE_INFO("SNMP message sent (%" PRIuSIZE " bytes)...\r\n", context->response.messageLen);
//Display the contents of the SNMP message
TRACE_DEBUG_ARRAY(" ", context->response.message, context->response.messageLen);
//Display ASN.1 structure
error = asn1DumpObject(context->response.message, context->response.messageLen, 0);
//Any error to report?
if(error) return error;
//Send SNMP response message
error = socketSendTo(context->socket, &context->remoteIpAddr, context->remotePort,
context->response.message, context->response.messageLen, NULL, 0);
//Return status code
return error;
}
