// Too complicated to be inline
Result
ExpectTagAndGetLength(Input& input, uint8_t expectedTag, uint16_t& length)
{
PR_ASSERT((expectedTag & 0x1F) != 0x1F); // high tag number form not allowed
uint8_t tag;
if (input.Read(tag) != Success) {
return Failure;
}
if (tag != expectedTag) {
return Fail(SEC_ERROR_BAD_DER);
}
// The short form of length is a single byte with the high order bit set
// to zero. The long form of length is one byte with the high order bit
// set, followed by N bytes, where N is encoded in the lowest 7 bits of
// the first byte.
uint8_t length1;
if (input.Read(length1) != Success) {
return Failure;
}
if (!(length1 & 0x80)) {
length = length1;
} else if (length1 == 0x81) {
uint8_t length2;
if (input.Read(length2) != Success) {
return Failure;
}
if (length2 < 128) {
// Not shortest possible encoding
return Fail(SEC_ERROR_BAD_DER);
}
length = length2;
} else if (length1 == 0x82) {
if (input.Read(length) != Success) {
return Failure;
}
if (length < 256) {
// Not shortest possible encoding
return Fail(SEC_ERROR_BAD_DER);
}
} else {
// We don't support lengths larger than 2^16 - 1.
return Fail(SEC_ERROR_BAD_DER);
}
// Ensure the input is long enough for the length it says it has.
return input.EnsureLength(length);
}
