Re: DalSemi: Add-Only Memory for Storage of Digital Cash (fwd)
Perhaps someone with more semiconductor physics background can correct me, but my understanding is that some kinds of nuclear radiation can be used to erase OTP EPROMS. I suppose this might damage the crystal lattice badly enough to render the device useless in some bit positions or reduce data retention time a lot, but I sure wouldn't bet any security on devices out there not being arbitrarily reprogrammable (thus using bits to represent digital coins in a wallet that get reset when they are spent is not a good idea).
You might want to take a look at the paper I mentioned, then: I believe that irradiation of the OTP EPROM to return all bits to "ones" is too blunt a tool to do you any good. A virgin EPROM has a value of zero in the suggested scheme. And, as mentioned, flipping random sets of bits is strongly likely to get you caught. Note also that the encoding is strongly tied to the laser-etched serial number on the chip, so replay attacks between two different chips -- i.e. copying a fully loaded chip to a virgin chip -- won't work. However, it does open up the scheme to replay attacks, if you can load the chip with value, spend it, irradiate it, and then successfully reprogram the chip with the exact same values you recorded. Good point. I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken? nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
I seem to remember PROMs actually undergoing physical, rather than electrical, state changes (that were presumably nonreversible). Am I recalling old technology, or am I just plain mistaken?
There are three technologies here (as I am sure you know), masked proms programmed at birth by metalization pattersns and not subject to non destructive change after they leave the foundary, fuse programable proms (which is basically a technology of the 70s to 80s) and CMOS proms that depend on patterns of trapped charge injected into insulating layers (crudely EPROMs and lots of cousins such as flash EPROMs, eraseable PALS and FPGAs etc). The old fashioned titanium fuse proms indeed did operate by having the fuse elements literally blown open by the programming process using higher voltages and special prgramming logic activated by the higher voltages that allowed a given fuse to be addressed individually and blown open (literally vaporized). This process is obviously one way (except in defective devices) and once a fuse has been blown (making a 1 in a blank device a zero for example or enabling a circuit path in a programmable logic device) there is nothing that can be done to reverse the process. Fuse programmable parts are usually bipolar devices. And for the most part fuse programmable proms are small and very fast and somewhat expensive and use lots of power. CMOS eprom technology (which has spread to many many kinds of programmable logic devices as CMOS has become faster and faster due to finer line geometries) depends on injecting pockets of charge into a silicon glass insulating layer. The electric field associated with these pockets of charge acts as the gate of FETS built on top of the insulating layer - turning on those transistors where there is charge and leaving those off where there is not. The classical UV eraseable version of this technology is erased by exposing the device to UV light which renders the silicon conductive which shorts out the trapped charge sites. A modern varient induces a controlled avalanche breakdown through the silicon insulator region which also shorts out the stored charge. The later version is eraseable without UV light by electrical action and is the technology used in many EEPROMs and Flash EPROMs. Thus the modern flash EPROM technology and its cousins in programmable logic allows many (hundreds to tens of thousands) of erasure and reprogramming (reinjectiong charge) cycles in modern prom devices. Dave Emery
nathan
participants (2)
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Dave Emery -
Nathan Loofbourrow