5. The important part is what they do and how they do it:
MD5sum and SHA1sum are hash functions - they take a piece of data, compact it and create a suitably unique output that is very hard to emulate with a different piece of data. They don't encrypt anything - you can't take MD5 or SHA output and "un hash" it to get back to your starting point. The difference between the two lies in what algorithm they use to create the hash. Also note that MD5sum is now broken as a way was discovered to easily generate collisions and should not be used nor trusted anymore. I would use SHA1sum due to MD5sum being out of date and no linger trusted.
6. Storing public keys or certificate files in the public domain is handled by Certificate Authorities (CAs). These authority servers are the same thing as a PKI server.
7. You will need to acquire the decryption key.
8. The Encrypting File System (EFS) is a component of the NTFS file system on Windows 2000, Windows XP Professional, and Windows Server 2003. (Windows XP Home doesn't include EFS.) EFS enables transparent encryption and decryption of files by using advanced, standard cryptographic algorithms. Any individual or program that doesn't possess the appropriate cryptographic key cannot read the encrypted data. Encrypted files can be protected even from those who gain physical possession of the computer that the files reside on. Even persons who are authorized to access the computer and its file system cannot view the data. While other defensive strategies should be used, and encryption isn't the correct countermeasure for every threat, encryption is a powerful addition to any defensive strategy. EFS are the built-in file encryption tool for Windows file systems.
9. BitLocker Drive Encryption is an FDE solution from Microsoft. It is included with the Ultimate and Enterprise editions of Windows Vista and Windows Seven, as well as Windows Server 2008 and Windows Server 2008 R2. By default it uses the AES encryption algorithm (CBC mode with a 128 bit key), combined with the Elephant diffuser for additional disk encryption.
BitLocker can be run in the following modes: * Transparent Operation Mode that is based on Trusted Platform Module (TPM) 1.2 support that allows the user to log onto Windows normally, as the disk encryption key is sealed by the TPM chip * User Authentication Mode that requires the user to provide authentication to the pre-boot environment (pre-boot PIN) * USB Key Mode that requires the user to insert a USB flash drive containing the decryptor key * Provides the end-user local Administration rights- presenting the opportunity to shut FDE off. The above-mentioned modes can be used either separately or combined as desired.

One of the disadvantages of BitLocker Drive Encryption is that it is not available on all Windows versions, so businesses that do not use Windows Vista and Windows Seven Enterprise and Ultimate editions need to look for a third-party FDE solution. Another disadvantage is that BitLocker gives the end user local admin rights which give the end user the ability to turn off the encryption functionality. Also, BitLocker does not provide reporting, so if a laptop goes missing it makes it nearly impossible to prove that it is indeed encrypted.
10. The use of encryption technology to protect computer data is growing—and that fact presents a challenge for forensic investigators. Without a decryption key, forensic tools cannot be used to find digital evidence. Even with the key, searching encrypted data can be tricky and time consuming. Below are some answers to common questions about trends in the use of encryption and what investigators can do to get as much evidence as possible from an encrypted file or drive.