1. A digital content encryption method, wherein:
an encryption apparatus divides digital content into a plurality of areas, and respectively assigns session keys different from one another to the areas generated by the division;
the session keys assigned to the respective areas are used for encrypting the areas concerned;
a pair of a public key and a private key according to public-key cryptography is assigned to each set of at least one user who uses the digital content that has been encrypted, each pair of the public key and the private key being different from other pairs;
for each area, the session key assigned to that area is encrypted with the public key assigned to the set of at least one user who is permitted to browse the area in question; and
encrypted digital content comprising the plurality of encrypted areas and the encrypted session keys, at least one of which is generated for each areas, is outputted.
2. A digital content encryption method according to claim 1, wherein:
header information of the encrypted digital content includes, as partitioning information, information indicating dividing positions of the digital content, and information indicating which user can decrypt which encrypted area in the encrypted digital content.
3. A digital content encryption method according to claim 1, wherein:
at least one same user is included in a plurality of the sets each formed of at least one user.
4. A digital content encryption method according to claim 1, wherein:
in cases in which an inclusive relation between the user and the at least one set is expressed by associating the user with a leaf of a tree and by associating the at least one set to which the user belongs with a node and a root of the tree, a key management apparatus assigns a public key and a private key corresponding to the public key to the leaf, the node and the root, with each pair of a public key and a private key being different from other pairs;
different private keys assigned respectively to a leaf corresponding to one user, the root, and nodes existing on a path connecting the leaf and the root, are delivered as decryption keys to the user corresponding to the leaf; and
the public keys corresponding to the private keys delivered to the user are made public as encryption keys corresponding to the decryption keys.
5. A digital content encryption method according to claim 1, wherein:
the encryption apparatus generates a digital signature corresponding to the encrypted areas, or to the encrypted areas and the encrypted session keys, and gives the generated digital signature to the encrypted areas, or to the encrypted areas and the encrypted session keys.
6. A digital content decryption method for digital content that has been encrypted according to the method of claim 1, wherein:
a decryption apparatus uses a private key, provided from the user to the decryption apparatus, to decrypt the session key that has been encrypted with the public key corresponding to the private key, and uses the decrypted session key to decrypt the area that has been encrypted with the session key; and
displays the decrypted area, and displays blacked out the areas that are not decrypted by the decryption apparatus.
7. A digital content decryption method for digital content that has been encrypted according to claim 5, wherein:
the decryption apparatus validates the given digital signature to examine whether the encrypted digital content has been altered or not.
8. A workflow system comprising an encryption apparatus and a plurality of decryption apparatuses, wherein:
the encryption apparatus divides digital content into a plurality of areas depending on kinds of information;
the encryption apparatus comprises a means which encrypts the areas of the divided digital content with encryption keys different for each area; and
each of the decryption apparatuses comprises: a means which decrypts a specific area of the encrypted digital content, and further comprises a means which transmits the encrypted digital content to another decryption apparatus.
9. A workflow system according to claim 8, wherein:
the workflow system comprises a key management apparatus that has a function of distributing suitable decryption keys to the decryption apparatuses depending on users of the decryption apparatuses; and
the key management apparatus comprises a means which makes public encryption keys corresponding to the decryption keys, to the encryption apparatus.
10. A workflow system according to claim 8, wherein:
the encryption apparatus has a function of giving digital signature to the encrypted digital content; and
each of the decryption apparatuses has a function of examining whether the digital content has been altered or not, by validating the encrypted digital content given the digital signature.
11. An encryption method according to claim 1, wherein:
the encryption apparatus constructs, for each user, a session key set including session keys used for encrypting respective areas that can be browsed by the user in question; and
the encryption apparatus encrypts the session key sets for each user, using the public key according to the public-key cryptography, assigned to each user.
12. An encryption method according to claim 11, wherein:
the encryption apparatus generates an order control random value for a first user;
the encryption apparatus encrypts a first session key set constructed for the first user and the order control random value generated for the first user, using the public key according to the public-key cryptography assigned to the first user; and
a result of the encryption is taken as an order control random value for a second user, and the order control random value is used for encrypting a second session key set for the second user, the second session key set being different from the first session key set.
13. A decryption method corresponding to the encryption method according to claim 12, wherein:
a decryption apparatus:
decrypts the order control random value of the second user, using a private key provided from the second user to the decryption apparatus;
divides a result of the decryption into the order control random value of the first user and the second session key set;
decrypts areas that have been encrypted with session keys obtained from the second session key set; and
generates the encrypted digital content from the order control random value of the first user and the encrypted areas.
14. An encryption method according to claim 12, wherein:
a plurality of second order control random values are generated by applying threshold secret sharing processing to the order control random value;
the session keys are encrypted with respect to each of the second order control random values;
a set of results of the encryption of the session keys is taken as the order control random value for the second user.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A nitride semiconductor device comprising:
a stacked foundation layer formed on an AlN buffer layer formed on a silicon substrate, the stacked foundation layer including a plurality of AlN foundation layers and a plurality of GaN foundation layers being alternately stacked with the AlN foundation layers; and
a functional layer including:
a low-concentration part provided on the stacked foundation layer, the low-concentration part including a nitride semiconductor and having a Si concentration less than 1\xd71018 cm\u22123; and
a high-concentration part provided on the low-concentration part and having a Si concentration not less than 1\xd71018 cm\u22123,
a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers including:
a first portion having a Si concentration less than 5\xd71018 cm\u22123;
a second portion having a Si concentration less than 5\xd71018 cm\u22123; and
a third portion being provided between the first portion and the second portion, the third portion having a Si concentration not less than 5\xd71018 cm\u22123 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.
2. The device according to claim 1, wherein
the thickness of the third portion is not less than 0.1 nanometers and not more than 50 nanometers.
3. The device according to claim 1, wherein
all of the GaN foundation layers except for the substrate-side GaN foundation layer among the plurality of GaN foundation layers have a Si concentration less than 5\xd71018 cm\u22123.
4. The device according to claim 1, wherein
a thickness of the high-concentration part is not less than 1.5 micrometers and not more than 4 micrometers.
5. The device according to claim 1, wherein
the functional layer further includes:
a light emitting part provided on the high-concentration part and having a plurality of barrier layers and a plurality of well layers, the each of the well layers being provided between the barrier layers; and
a p-type semiconductor layer provided on the light emitting part, the p-type semiconductor layer including a nitride semiconductor and containing at least one of Mg, Zn and C.
6. A nitride semiconductor device comprising
a functional layer formed on an AlN buffer layer formed on a silicon substrate, the functional layer including:
a plurality of low-concentration parts including a nitride semiconductor and having a Si concentration less than 5\xd71018 cm\u22123; and
a plurality of high-concentration parts having a Si concentration not less than 5\xd71018 cm\u22123, the low-concentration parts being alternately stacked with the high-concentration parts,
a thickness of each of the high-concentration parts being smaller than a thickness of each of the low-concentration parts,
each of the high-concentration parts includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
7. The device according to claim 6, wherein
the thickness of each of the high-concentration parts is not less than 0.1 nanometers and not more than 50 nanometers.
8. The device according to claim 6, further comprising
a stacked foundation layer formed on the AlN buffer layer and under the functional layer,
the stacked foundation layer including a plurality of AlN foundation layers and a plurality of GaN foundation layers being alternately stacked with the AlN foundation layers, and
a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers including:
a first portion having a Si concentration less than 5\xd71018 cm\u22123;
a second portion having a Si concentration less than 5\xd71018 cm\u22123;and
a third portion provided between the first portion and the second portion, the third portion having a Si concentration not less than 5\xd71018 cm\u22123 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.
9. A nitride semiconductor wafer comprising:
a silicon substrate;
an AlN buffer layer provided on the silicon substrate;
a stacked foundation layer provided on the AlN buffer layer, the stacked foundation layer including a plurality of AlN foundation layers and a plurality of GaN foundation layers being alternately stacked with the AlN foundation layers; and
a functional layer including
a low-concentration part provided on the stacked foundation layer, the low-concentration part including a nitride semiconductor and having a Si concentration less than 5\xd71018 cm\u22123, and
a high-concentration part provided on the low-concentration part and having a Si concentration not less than 5\xd71018 cm\u22123,
a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers including:
a first portion having a Si concentration less than 5\xd71018 cm\u22123;
a second portion having a Si concentration less than 5\xd71018 cm\u22123; and
a third portion provided between the first portion and the second portion, the third portion having a Si concentration not less than 5\xd71018 cm\u22123 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.
10. The wafer according to claim 9, wherein
the thickness of the third portion is not less than 0.1 nanometers and not more than 50 nanometers.
11. The wafer according to claim 9, wherein
all of the GaN foundation layers except for the substrate-side GaN foundation layer among the plurality of GaN foundation layers have a Si concentration less than 5\xd71018 cm\u22123.
12. The wafer according to claim 9, wherein
a thickness of the high-concentration part is not less than 1.5 micrometers and not more than 4 micrometers.
13. The wafer according to claim 9, wherein
the functional layer further includes:
a light emitting part provided on the high-concentration part and having a plurality of barrier layers and a plurality of well layers, the each of the well layers being provided between the barrier layers; and
a p-type semiconductor layer provided on the light emitting part, the p-type semiconductor layer including a nitride semiconductor and containing at least one of Mg, Zn and C.
14. A nitride semiconductor wafer comprising:
a silicon substrate;
an AlN buffer layer provided on the silicon substrate; and
a functional layer provided on the AlN buffer layer,
the functional layer including:
a plurality of low-concentration parts including a nitride semiconductor and having a Si concentration less than 5\xd71018 cm\u22123; and
a plurality of high-concentration parts having a Si concentration not less than 5\xd71018 cm\u22123, the low-concentration parts being alternately stacked with the high-concentration parts,
a thickness of each of the high-concentration parts is smaller than a thickness of each of the low-concentration parts,
each of the high-concentration parts includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
15. The wafer according to claim 14, wherein
the thickness of each of the high-concentration parts is not less than 0.1 nanometers and not more than 50 nanometers.
16. The wafer according to claim 14, further comprising
a stacked foundation layer formed on the AlN buffer layer and under the functional layer,
the stacked foundation layer including a plurality of AlN foundation layers and a plurality of GaN foundation layers being alternately stacked with the AlN foundation layers, and
a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers including:
a first portion having a Si concentration less than 5\xd71018 cm\u22123;
a second portion having a Si concentration less than 5\xd71018 cm\u22123;and
a third portion provided between the first portion and the second portion, the third portion having a Si concentration not less than 5\xd71018 cm\u22123 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.
17. A method for manufacturing a nitride semiconductor layer comprising:
forming a stacked foundation layer by alternately stacking a plurality of AlN foundation layers and a plurality of GaN foundation layers on an AlN buffer layer provided on a silicon substrate; and
forming a functional layer by forming a low-concentration part on the stacked foundation layer and forming a high-concentration part on the low-concentration part, the low-concentration part including a nitride semiconductor and having a Si concentration less than 5\xd71018 cm\u22123, the high-concentration part having a Si concentration not less than 5\xd71018 cm\u22123,
in formation of a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers, the forming the stacked foundation layer includes forming
a first portion having a Si concentration less than 5\xd71018 cm\u22123,
a second portion having a Si concentration less than 5\xd71018 cm\u22123 and
a third portion provided between the first portion and the second portion, the third portion having a Si concentration not less than 5\xd71018 cm\u22123 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.
18. The method according to claim 17, wherein
the thickness of the third portion is not less than 0.1 nanometers and not more than 50 nanometers.
19. A method for manufacturing a nitride semiconductor layer comprising:
forming a functional layer on an AlN buffer layer formed on a silicon substrate,
the forming the functional layer including repeating a process a plurality of times, the process including:
forming a low-concentration part including a nitride semiconductor and having a Si concentration less than 5\xd71018 cm\u22123; and
forming a high-concentration part having a Si concentration not less than 5\xd71018 cm\u22123, and
a thickness of each of the high-concentration parts is smaller than a thickness of each of the low-concentration parts,
each of the high-concentration parts includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
20. The method according to claim 19, wherein
the thickness of each of the high-concentration parts is not less than 0.1 nanometers and not more than 50 nanometers.
21. The device according to claim 1, wherein the third portion includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
22. The wafer according to claim 9, wherein the third portion includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
23. The wafer according to claim 17, wherein the third portion includes Si\u03b1N\u03b2(0<\u03b1, 0<\u03b2).
24. The device according to claim 6, wherein the thickness of each of the low-concentration parts is not less than 50 nanometers and not more than 500 nanometers.
25. The device according to claim 6, wherein the thickness of each of the low-concentration parts is not less than 300 nanometers and not more than 500 nanometers.
26. The wafer according to claim 14, wherein the thickness of each of the low-concentration parts is not less than 50 nanometers and not more than 500 nanometers.
27. The wafer according to claim 14, wherein the thickness of each of the low-concentration parts is not less than 300 nanometers and not more than 500 nanometers.
28. The method according to claim 19, wherein the thickness of each of the low-concentration parts is not less than 50 nanometers and not more than 500 nanometers.
29. The method according to claim 19, wherein the thickness of each of the low-concentration parts is not less than 300 nanometers and not more than 500 nanometers.