Digital signal conversion enabling to find unauthorized change of the signal

A method of processing a digital signal, comprising steps of:

• replacing a bit "0" in the digital signal with a first n-bit length binary coded signal including at least one bit of "0" and also replacing a bit "1" in the digital signal with a second n-bit length binary coded signal including at least one bit of "0", wherein n is an integer equal to or greater than two and wherein the first n-bit length binary coded signal and the second n-bit length binary coded signal are different from each other and
• writing in a non-rewritable recording medium the replaced binary coded signals in accordance with the bits constituting the digital signal,
• wherein n is equal to two and wherein one of "01" and "10" is assigned to the first n-bit length binary coded signal and a remaining one of "01" and "10" is assigned to the second n-bit length binary coded signal,
• wherein the recording medium comprises first and second recording disks which are coaxially supported on a rotating shaft, and wherein each of the first and second n-bit length binary coded signals is written in the first and second recording disks such that upper significant bits in the first and second n-bit length binary coded signals are recorded in the first recording disk, and lower significant bits in the first and second n-bit length binary coded signals are recorded in the second recording disk.

A method of processing a digital signal, comprising steps of:

• replacing a bit "0" in the digital signal with a first n-bit length binary coded signal including at least one bit of "0" and also replacing a bit "1" in the digital signal with a second n-bit length binary coded Signal including at least one bit of "0", wherein n is an integer equal to or greater than two and wherein the first n-bit length binary coded signal and the second n-bit length binary coded signal are different from each other;
• and
• writing in a non-rewritable recording medium the replaced binary coded signals in accordance with the bits constituting the digital signal
• wherein n is equal to three and wherein one of "001", "110" and "101" is assigned to the first n-bit length binary coded signal and a remaining one of "001", "110" and "101" is assigned to the second n-bit length binary coded signal
• wherein the recording medium comprises first, second and third recording disks which are coaxially supported on a rotating shaft, and wherein each of the first and second n-bit length binary coded signals is written in the first, second and third recording disks such that lowest significant bits in the first and second n-bit length binary coded signals are recorded in the first recording disk, intermediately significant bits in the first and second n-bit length binary coded signals are recorded in the second recording disk, and highest significant bits in the first and second n-bit length binary coded signals are recorded in the third recording disk.

A method of recording a digital signal, comprising the steps of:

• recording the digital signal in a non-rewritable recording medium, the digital signal containing plural pieces of information;
• further recording a header in the recording medium, the header containing at least one of information items regarding a bit length of the digital signal, and number of bits of a predetermined kind contained in the digital signal,
• wherein a bit "0" in the digital signal is replaced with a first n-bit length binary coded signal including at least one bits of "0" and also a bit "1" in the digital signal is replaced with a second n-bit length binary coded signal including at least one bit of "0", wherein n is an integer equal to or greater than two, and
• wherein the first n-bit length binary coded signal and the second n-bit length binary coded signal are different from each other, and the first and second n-bit length binary coded signals are written in a non-rewritable recording medium in accordance with the bits constituting the digital signal.

A method of checking a data status in a non-rewritable recording medium, wherein a bit "0" in the digital signal is replaced with a first n-bit length binary coded signal including at least one bit of "0" and also a bit "1" in the digital signal is replaced with a second n-bit length binary coded signal including at least one bit of "0" wherein n is an integer equal to or greater then two and the first and second n-bit length binary coded signals are different from each other and wherein a bit "0" in The first and second n-bit length binary coded signals does not change a status of the recording medium when written in the recording medium whereas a bit "1" in the first and second n-bit length binary coded signals changes the status of the recording medium when written in the recording medium, the method comprising the steps of:

• (a) reading the signals written in the recording medium on an n-bit basis;
• (b) checking whether or not bits in all digit positions of the n-bit signals read in step (a) are "1";
• and
• (c) determining that The signals in the recording medium have been changed when a result of checking in step (b) is affirmative.

A method of checking a data status in a non-rewritable recording medium, wherein a bit "0" in a digital signal is replaced with one of three-bit length binary coded signals selected from "001", "110" and "101" and also a bit "1" in the digital signal is replaced with one of non-selected binary coded signals, and wherein the replaced binary coded signals are written in a non-rewritable recording medium in accordance with the bits constituting the digital signal wherein a bit "0" of the replaced binary coded signals does not change a status of the recording medium when written in the recording medium whereas a bit "1" of the replaced binary coded signals changes the status of the recording medium when written in the recording medium, the method comprising the steps of:

• (a) reading the signals written in the recording medium on a three-bit basis;
• (b) checking whether or not three-bit signals read in step (a) are "111";
• and
• (c) determining that the signals in the recording medium have been changed when a result of checking in step (b) is affirmative.

A method of checking a data status in a non-rewritable recording medium, wherein a bit "0" in a digital signal is replaced with one of two-bit length binary coded signals selected from "01" and "10" and also a bit "1" in the digital signal is replaced with non-selected binary coded signals, and wherein the replaced binary coded signals are written in the recording medium in accordance with the bits constituting the digital signal wherein a bit "0" of the replaced binary coded signals does not change a status of the recording medium when written in the recording medium whereas a bit "1" of the replaced binary coded signals changes the status of the recording medium when written in the recording medium, the method comprising the steps of:

• (a) reading the signals written in the recording medium on a two-bit basis;
• (b) checking whether or not two-bit signals read in step (a) are "11";
• and
• (c) determining that the signals in the recording medium have been changed when a result of checking in step (b) is affirmative.