Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Central trusted authority provides computer authentication
Reexamination Certificate
1998-03-04
2001-10-23
Peeso, Thomas R. (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Central trusted authority provides computer authentication
C713S159000, C713S161000, C713S172000, C713S175000
Reexamination Certificate
active
06308266
ABSTRACT:
TECHNICAL FIELD
This invention relates to products that employ cryptographic functionality. More particularly, this invention relates to an architecture that enables a user of such products to enable various grades of cryptography strength in those products.
BACKGROUND
Cryptographic ciphers are often measured and described in terms of their strength. Different ciphers offer different strength depending on how hard they are to break. “Strong” ciphers are more difficult to break than “weak” ciphers. Different types of data lend themselves to different strengths of cryptography. For instance, if the cost required to break a cipher is greater than the value of the protected data, that particular cipher is most likely appropriate for the data even though the cipher may be relatively weak compared to other ciphers. If the time required to break a cipher is longer than the time needed to keep the protected data secret, the cipher is properly suited for the data.
In public key cryptography, the cipher typically derives its strength from the length of the key used to encode the data. A “key” is a string of bits and its “length” is expressed in the number of bits in the string. The same cipher can be weak or strong depending upon the key length. A cipher with a comparatively short key length (e.g., 40 or 56 bits) may be considered weak, whereas the same cipher with a comparatively long key length (e.g., 128 bits) may be deemed strong. It is common today for various software products to employ ciphers with 40-bit or 56-bit keys, which are generally characterized as weak, as well as ciphers that employ 128-bit keys, which are generally considered to be strong.
Because of their potential for illegal or improper use, cryptographic ciphers cannot be exported from the United States without approval from the U.S. government. Generally, products with “weak” ciphers having short key length may be exported. Such products are said to have “exportable strength” cryptographic functionality. Products with “strong” ciphers having long key lengths are usually not permitted to leave the country. To export a cryptographic product from the U.S., the product manufacturer or exporter must first obtain an export license from the U.S. government.
As a result of this government policy, the makers of cryptographically enhanced products face a dilemma. They would like to make a single product that can be sold in the U.S. and exported abroad without the hassle of securing special export licenses for each and every foreign market.
FIG. 1
illustrates this point. A cryptographic product provider
10
makes a single product
12
that utilizes cryptographic services, such as encryption, decryption, digital signing, and authentication. To enable global exportation to Europe and Asia without having to secure special export licenses, the provider
10
typically configures the product with a weak “exportable-strength” cipher. As a result, the U.S. version of the product is likewise pared down to the lowest exportable-strength cipher. However, some U.S. customers might request and be entitled to use higher strength ciphers. Such customers must submit special requests to the provider, along with proof of residence and proposed use, before the provider
10
can release a stronger version of the product.
Accordingly, there is a need to provide an improved technique for supplying cryptographically enhanced products throughout the world.
SUMMARY
This invention concerns an architecture that selectively exposes various grades of cryptographic strength in the same product. A product provider manufactures one cryptographically enhanced product that can be marketed to users in the U.S. and exported to users abroad. Once installed, the product initially exposes only a low-level, exportable-strength cryptography that may be used in both the U.S. or overseas with a general export license. Stronger cryptography is implemented in the product, but is not exposed to the user. It is also not required to expose by default all algorithms supported by the cryptographic product. It is possible to use this same mechanism to only expose the existence of an algorithm when authorized to do so.
To enable the stronger cryptography with the product, the user must first obtain a certificate that contains the capabilities to expose the stronger cryptography in the product. The certificate is issued to the user from a certifying authority. The certifying authority, in turn, obtains the enabling capabilities from the product provider. The process of requesting and receiving the certificate enables the product provider to ensure that the certifying authority, and ultimately the user, is legally able to employ the stronger cryptography in the product.
According to one implementation, the certifying authority submits a request to the product provider for higher strength cryptography. The request contains an identity certificate that uniquely identifies the certifying authority. The product provider authenticates the identity certificate and verifies whether the certifying authority can use higher strength cryptography. The product provider may evaluate such policy considerations as where the certifying authority resides, to whom the certifying authority intends to issue certificate, and the purpose for which the enhanced strength product is to be used. If the policy considerations are met, the product provider creates a token that contains the capabilities to enable the higher strength cryptography within the product. The token should have a means of verifying the integrity of the token such as a digital signature to ensure that any attempt to alter the token can be detected. The token also contains a hash digest of the identity certificate, thereby binding the certifying authority to the enabling token.
When the user desires higher strength cryptography, the user submits a request to the certifying authority for the higher strength cryptography. The request contains the user's public key. The certifying authority authenticates the user and determines whether the user can use the higher strength cryptography. The certifying authority may have its own set of policy considerations such as where the user is located, the purpose for using the higher strength cryptography, and so on. If the policy parameters are satisfied, the certifying authority creates a certificate that contains the certifying authority identity and the signed token issued by the product provider. The certifying authority returns the certificate with the signed token to the user, where it is stored locally on the user's computer.
When the user desires the extra strength cryptography from the product, the certificate containing the signed token is passed into the product. The cryptographic product evaluates the certificate and signed token in several ways. First, the product verifies that the certificate is truly from the certifying authority. Second, the product verifies that the signed token is truly from the product provider. Third, the product ensures that the signed token contains the hash digest of the certifying authority, thereby linking the certifying authority with the product provider. Fourth, the product determines whether the certificate or signed token has expired. Fifth, the product determines whether the certificate or token has been revoked.
If all verification steps return true, the product uses the capabilities included in the signed token to expose the higher strength cryptography to the user. On the other hand, if any step returns false, the product denies the request for higher strength cryptography and continues to use only the low strength cryptography.
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patent:
Lee & Hayes PLLC
Microsoft Corporation
Peeso Thomas R.
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