(Even if the input is fully specified by the decompressor, these can result from false and multi-cycle paths, for example.) Another design criteria for the test result compressor is that it should give good diagnostic capabilities, not just a yes/no answer. The compactor must be synchronized with the data decompressor, and must be capable of handling unknown (X) states. Therefore, a test response compactor is also required, which must be inserted between the internal scan chain outputs and the tester scan channel outputs. With a large number of test chains, not all the outputs can be sent to the output pins. Experimental results show that for industrial circuits with test vectors and responses with very low fill rates, ranging from 3% to 0.2%, the test compression based on this method often results in compression ratios of 30 to 500 times. One common choice is a linear finite state machine, where the compressed stimuli are computed by solving linear equations corresponding to internal scan cells with specified positions in partially specified test patterns. Many different decompression methods can be used. At the same time, it might be desirable to store compressed data or. These chains are then driven by an on-chip decompressor, usually designed to allow continuous flow decompression where the internal scan chains are loaded as the data is delivered to the decompressor. Some clients do not handle responses with the gzip encoding method. In general, the idea is to modify the design to increase the number of internal scan chains, each of shorter length. Test compression takes advantage of the small number of significant values to reduce test data and test time. Loading and unloading these vectors is not a very efficient use of tester time. The rest of the scan chain is don't care, and are usually filled with random values. When an ATPG tool generates a test for a fault, or a set of faults, only a small percentage of scan cells need to take specific values. Test compression was developed to help address this problem. However, as chips got bigger and more complex the ratio of logic to be tested per pin increased dramatically, and the volume of scan test data started causing a significant increase in test time, and required tester memory. These techniques were very successful at creating high-quality vectors for manufacturing test, with excellent test coverage. It proved very difficult to get good coverage of potential faults, so Design for testability (DFT) based on scan and automatic test pattern generation (ATPG) were developed to explicitly test each gate and path in a design. The first ICs were tested with test vectors created by hand. If you do find such samples, please submit them! Thanks!ī DidierStevensLabs.Test compression is a technique used to reduce the time and cost of testing integrated circuits. It wouldn't surprise me if these formats starts to be used to deliver malware in a near future. There are more formats like DAA: GBI, ISZ. It looks like the DAA format consists of an ISO file chopped up in chunks of 65536 bytes, that are then compressed.Īnd then, I decompress all chunks to be identified by file-magic.py: My tool found sequences of Zlib compressed chunks, that decompress to streams of 64K bytes long (65536). It's not ready for publication yet, but I had good results with this DAA sample: Not a tool to parse DAA files, but a more generic tool: a tool that scans through binary data for known compression methods and extracts the compressed data it finds. Like DAA2ISO.Īnd I started to make my own tool in Python. Most LZ77 derived algorithms split input data into blocks of uncompressed data (called. There are free, open source tools to convert DAA files to ISO (e.g. Helper class for compression algorithms that use the ideas of LZ77. I did some research, and found out that the DAA format is, in a nutshell, a header followed by chunks of a compressed ISO file. I doubt that these campaigns will make a lot of victims, if any: I don't think you'll find many corporate users that are familiar with SWIFT messages and have a tool like PowerISO installed. If you don't, you can't open the DAA file to execute the embedded EXE file. This is exactly like the attacks we reported with ISO files, except that in this case, you definitively need the right application to be able to execute the embedded malware. I have a license for such an application, and was able to extract the content: a single. Only Windows machines with installed image editing applications (like PowerISO) can open these files. Unlike ISO files, DAA files are not recognized by Windows, they won't be mounted when double clicked. Reader Jason submitted a suspicious file he received via email: attachment Swift Detail.daaĪfter a quick Google search, I found out DAA stands for Direct Access Archive and that it is a disk image format like ISO files.
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