Figure provided to the author by Phil Zimmermann. in .NET Produce QR Code JIS X 0510 in .NET Figure provided to the author by Phil Zimmermann.

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Figure provided to the author by Phil Zimmermann. using .net framework tocreate qr code on web,windows application GS1 DataBar Family CHAPTER 7 / ELECTRONIC MAIL SECURITY G H I J K L M N O P X Y Visual Studio .NET QR unknown signatory X is signed by Y key"s owner is trusted by you to sign keys key"s owner is partly trusted by you to sign keys key is deemed legitimate by you S Q R. Figure 7.7 PGP Trust Model Example Several po qr-codes for .NET ints are illustrated in Figure 7.7.

1. Note that all keys whose owners are fully or partially trusted by this user have been signed by this user, with the exception of node L. Such a user signature is not always necessary, as the presence of node L indicates, but in practice, most users are likely to sign the keys for most owners that they trust.

So, for example, even though E s key is already signed by trusted introducer F, the user chose to sign E s key directly. 2. We assume that two partially trusted signatures are sufficient to certify a key.

Hence, the key for user H is deemed legitimate by PGP because it is signed by A and B, both of whom are partially trusted. 3. A key may be determined to be legitimate because it is signed by one fully trusted or two partially trusted signatories, but its user may not be trusted to sign other keys.

For example, N s key is legitimate because it is signed by E, whom this user trusts, but N is not trusted to sign other keys because this user has not assigned N that trust value. Therefore, although R s key is signed by N, PGP does not consider R s key legitimate. This situation makes perfect sense.

If you wish to send a private message to some individual, it is not necessary that you trust that individual in any respect. It is only necessary that you are sure that you have the correct public key for that individual. 4.

Figure 7.7 also shows an example of a detached orphan node S, with two unknown signatures. Such a key may have been acquired from a key server.

. 7.2 / S/MIME PGP cannot .net vs 2010 QR Code 2d barcode assume that this key is legitimate simply because it came from a reputable server. The user must declare the key legitimate by signing it or by telling PGP that it is willing to trust fully one of the key s signatories.

A final point: Earlier it was mentioned that multiple user IDs may be associated with a single public key on the public-key ring. This could be because a person has changed names or has been introduced via signature under multiple names, indicating different e-mail addresses for the same person, for example. So we can think of a public key as the root of a tree.

A public key has a number of user IDs associating with it, with a number of signatures below each user ID. The binding of a particular user ID to a key depends on the signatures associated with that user ID and that key, whereas the level of trust in this key (for use in signing other keys) is a function of all the dependent signatures. REVOKING PUBLIC KEYS A user may wish to revoke his or her current public key either because compromise is suspected or simply to avoid the use of the same key for an extended period.

Note that a compromise would require that an opponent somehow had obtained a copy of your unencrypted private key or that the opponent had obtained both the private key from your private-key ring and your passphrase. The convention for revoking a public key is for the owner to issue a key revocation certificate, signed by the owner. This certificate has the same form as a normal signature certificate but includes an indicator that the purpose of this certificate is to revoke the use of this public key.

Note that the corresponding private key must be used to sign a certificate that revokes a public key. The owner should then attempt to disseminate this certificate as widely and as quickly as possible to enable potential correspondents to update their public-key rings. Note that an opponent who has compromised the private key of an owner can also issue such a certificate.

However, this would deny the opponent as well as the legitimate owner the use of the public key, and therefore, it seems a much less likely threat than the malicious use of a stolen private key..
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