// 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); }