Scanning - 1 1 Computer Security Basic Networking Concepts...

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Unformatted text preview: 1 1 Computer Security Basic Networking Concepts and Network Hacking Original slides prepared by K. Liszka, Original slides prepared by K. Liszka, The University of Akron The University of Akron for 3460:453/553 for 3460:453/553 2 Binary Numbering System • Uses the number 2 as its base • Binary digits (bits): 0 and 1 • Byte – Group of 8 bits – Can represent 2 8 = 256 different values UNIX and Linux Permissions • UNIX and Linux File permissions are represented with bits – 0 means removing the permission – 1 means granting the permission – 111 (rwx) means all permissions apply 3 Determining Binary Values • Each position represents a power of 2 value – Usually the bit on the right is the least significant bit • Converting 1011 to decimal – 1 x 2 = 1 – 1 x 2 1 = 2 – 0 x 2 2 = 0 – 1 x 2 3 = 8 • 1 + 2 + 8 = 11 (decimal value) 3 2 1 0 4 Understanding Nibbles • Half a byte or four bits • Helps with reading the number by separating the byte – 1111 1010 • Components – High-order nibble (left side) – Low-order nibble (right side) • Converting 1010 1010 to decimal – Low-order nibble • 1010 = 10 (base 10) – Multiply high-order nibble by 16 • 1010 = 10 x 16 = 160 (base 10) – 160 + 10 = 170 (base 10) 5 Octal Numbering System • Uses 8 as its base. – Supports digits from 0 to 7 • Octal digits can be represented with ______ bits. • Permissions on UNIX – Owner permissions (rwx) – Group permissions (rwx) – Other permissions (rwx) • Example: 111 101 001 – Octal representation 751 three 6 Hexadecimal Numbering System • Uses 16 as its base – Support numbers from 0 to 15 • Hex number consists of two characters – Each character represents a nibble – Value contains alphabetic letters (A … F) • A representing 10 and F representing 15 • Sometimes expressed with “0x” in front. 2 7 What’s an IP address (really)? • 32-bit decimal number normally written as four numbers between 1 and 255. – 8 bits / 1 byte / 1 octet • Separated by dots. – dotted-decimal notation 8 ping • A computer network tool used to test whether a particular host is reachable across an IP network. • Sends ICMP “echo request packets” to the target host. • Listens for ICMP “echo response” replies. ping pong 9 Fancier Tools • SuperScan – www.foundstone.com • NetScanTools Pro – Windows: www.netscantools.com – UNIX: www.fping.com 10 Classy IP addresses 240.0.0.0 – 255.255.255.255 E 224.0.0.0 – 239.255.255.255 D 192.0.0.0 – 223.255.255.255 C 128.0.0.0 – 191.255.255.255 B 0.0.0.0 – 126.255.255.255 A Range Class 11 Class A addresses XXX .XXX.XXX.XXX network ID (8 bits) host ID (24 bits) reserved for large corporations and governments reserved for large corporations and governments 12 Class B addresses XXX . XXX .XXX.XXX network ID (16 bits) host ID (16 bits) assigned to large corporations and Internet Service Providers assigned to large corporations and Internet Service Providers 3...
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Scanning - 1 1 Computer Security Basic Networking Concepts...

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