Commit `f1f35bd407`

f1f35bd4070c7dd0d232c5a3f2f7373511475565

parent: ceb109db05

Unsigned

cmc <hello@cleberg.net> · 2025-11-12 01:42 UTC

fix grammar in 2018 posts

Layout: unified · split

content/blog/2018-11-28-aes-encryption.org +45 −44

	@@ -6,15 +6,15 @@
6	* Basic AES	6	* Basic AES
7		7
8	If you're not familiar with encryption techniques, [[https://en.wikipedia.org/wiki/Advanced_Encryption_Standard][AES]] is the *Advanced	8	If you're not familiar with encryption techniques, [[https://en.wikipedia.org/wiki/Advanced_Encryption_Standard][AES]] is the *Advanced
9	Encryption Standard*. This specification was established by the National	9	Encryption Standard*. The National Institute of Standards and Technology
10	Institute of Standards and Technology, sub-selected from the Rijndael family of	10	established this specification, sub-selected from the Rijndael family of ciphers
11	ciphers (128, 192, and 256 bits) in 2001. Furthering its popularity and status,	11	(128, 192, and 256 bits) in 2001. Furthering its popularity and status, the US
12	the US government chose AES as their default encryption method for top-secret	12	government chose AES as their default encryption method for top-secret data,
13	data, removing the previous standard which had been in place since 1977.	13	removing the previous standard which had been in place since 1977.
14		14
15	AES has proven to be an extremely safe encryption method, with 7-round and	15	AES has proven to be a safe encryption method, with 7-round and 8-round attacks
16	8-round attacks making no material improvements since the release of this	16	making no material improvements since the release of this encryption standard
17	encryption standard almost two decades ago.	17	almost two decades ago.
18		18
19	#+begin_quote	19	#+begin_quote
20	Though many papers have been published on the cryptanalysis of AES, the fastest	20	Though many papers have been published on the cryptanalysis of AES, the fastest
	@@ -26,12 +26,13 @@ slightly more powerful than those proposed 10 years ago [23,24].
26		26
27	* How Secure is AES?	27	* How Secure is AES?
28		28
29	In theory, AES-256 is non-crackable due to the massive number of combinations	29	In theory, AES-256 (AES using a 256-bit key) is non-crackable due to the massive
30	that can be produced. However, AES-128 is no longer recommended as a viable	30	number of combinations that can the encryption process can produce. However,
31	implementation to protect important data.	31	AES-128 is no longer recommended as a viable implementation to protect important
		32	data due the 128-bit key's short length.
32		33
33	A semi-short [[http://www.moserware.com/2009/09/stick-figure-guide-to-advanced.html][comic strip]] from Moserware quickly explains AES for the public to	34	A semi-short [[http://www.moserware.com/2009/09/stick-figure-guide-to-advanced.html][comic strip]] from Moserware quickly explains AES for the public to
34	understand. Basically AES encrypts the data by obscuring the relationship	35	understand. Basically, AES encrypts the data by obscuring the relationship
35	between the data and the encrypted data. Additionally, this method spreads the	36	between the data and the encrypted data. Additionally, this method spreads the
36	message out. Lastly, the key produced by AES is the secret to decrypting it.	37	message out. Lastly, the key produced by AES is the secret to decrypting it.
37	Someone may know the method of AES, but without the key, they are powerless.	38	Someone may know the method of AES, but without the key, they are powerless.
	@@ -40,8 +41,8 @@ To obscure and spread the data out, AES creates a substitution-permutation
40	network. Wikipedia has a wonderful [[https://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/SubstitutionPermutationNetwork2.png/468px-SubstitutionPermutationNetwork2.png][example of an SP network]] available. This	41	network. Wikipedia has a wonderful [[https://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/SubstitutionPermutationNetwork2.png/468px-SubstitutionPermutationNetwork2.png][example of an SP network]] available. This
41	network sends the data through a set of S boxes (using the unique key) to	42	network sends the data through a set of S boxes (using the unique key) to
42	substitute the bits with another block of bits. Then, a P box will permutate, or	43	substitute the bits with another block of bits. Then, a P box will permutate, or
43	rearrange, the bits. This is done over and over, with the key being derived from	44	rearrange, the bits. This is performed numerous times, with the last round
44	the last round. For AES, the key size specifies the number of transformation	45	deriving the key. For AES, the key size specifies the number of transformation
45	rounds: 10, 12, and 14 rounds for 128-bit, 192-bit, and 256-bit keys,	46	rounds: 10, 12, and 14 rounds for 128-bit, 192-bit, and 256-bit keys,
46	respectively.	47	respectively.
47		48
	@@ -49,13 +50,13 @@ respectively.
49		50
50	1. KeyExpansion: Using [[https://en.m.wikipedia.org/wiki/Advanced_Encryption_Standard][Rijndael's key schedule]], the keys are dynamically	51	1. KeyExpansion: Using [[https://en.m.wikipedia.org/wiki/Advanced_Encryption_Standard][Rijndael's key schedule]], the keys are dynamically
51	generated.	52	generated.
52	2. AddRoundKey: Each byte of the data is combined with this key using bitwise	53	2. AddRoundKey: The process combines each byte of the data with the generated
53	xor.	54	key(s) using bitwise xor.
54	3. SubBytes: This is followed by the substitution of each byte of data.	55	3. SubBytes: Next, the process substitutes each byte of data.
55	4. ShiftRows: Then, the final three rows are shifted a certain number of	56	4. ShiftRows: Then, the process shifts the final three rows a specific number
56	steps, dictated by the cipher.	57	of steps, dictated by the cipher.
57	5. MixColumns: After the rows have been shifted, the columns are mixed and	58	5. MixColumns: Finally, the process mixes and combines the columns into the
58	combined.	59	final data for this round of processing.
59		60
60	This process does not necessarily stop after one full round. Steps 2 through 5	61	This process does not necessarily stop after one full round. Steps 2 through 5
61	will repeat for the number of rounds specified by the key. However, the final	62	will repeat for the number of rounds specified by the key. However, the final
	@@ -66,42 +67,42 @@ weakness).
66		67
67	According to research done by Bogdanov et al., it would take billions of years	68	According to research done by Bogdanov et al., it would take billions of years
68	to brute force a 126-bit key with current hardware. Additionally, this brute	69	to brute force a 126-bit key with current hardware. Additionally, this brute
69	force attack would require storing 2^{88} bits of data! However, there are a few	70	force attack would require storing 2^{88} bits of data! However, people have
70	different attacks that have been used to show vulnerabilities with the use of	71	shown different attacks displaying vulnerabilities with the use of this
71	this technology. Side-channel attacks use inadvertent leaks of data from the	72	technology. Side-channel attacks use inadvertent leaks of data from the hardware
72	hardware or software, which can allow attackers to obtain the key or run	73	or software, which can allow attackers to obtain the key or run programs on a
73	programs on a user's hardware.	74	user's hardware.
74		75
75	Please note that this is not something you should run out and try to implement	76	Please note that this is not something you should run out and try to implement
76	in your =Hello, World!= app after only a few hours of research. While AES	77	in your =Hello, World!= application after only hours of research. While AES
77	(basically all encryption methods) is extremely efficient in what it does, it	78	(basically all encryption methods) is efficient in what it does, it takes a lot
78	takes a lot of time and patience to understand. If you're looking for something	79	of time and patience to understand. If you're looking for something which
79	which currently implements AES, check out the [[https://www.bouncycastle.org/documentation.html][Legion of the Bouncy Castle]] for	80	currently implements AES, check out the [[https://www.bouncycastle.org/documentation.html][Legion of the Bouncy Castle]] for Java
80	Java implementations of cryptographic algorithms.	81	implementations of cryptographic algorithms.
81		82
82	* Why Does Encryption Matter?	83	* Why Does Encryption Matter?
83		84
84	There are limitless reasons to enable encryption at-rest or in-transit for	85	There are limitless reasons to enable encryption at-rest or in-transit for
85	various aspects of your digital life. You can research specific examples, such	86	aspects of your digital life. You can research specific examples, such as
86	as [[https://arstechnica.com/tech-policy/2018/12/australia-passes-new-law-to-thwart-strong-encryption/][Australia passes new law to thwart strong encryption]]. However, I will simply	87	[[https://arstechnica.com/tech-policy/2018/12/australia-passes-new-law-to-thwart-strong-encryption/][Australia passes new law to thwart strong encryption]]. However, I will simply
87	list a few basic reasons to always enable encryption, where feasible:	88	list basic reasons to always enable encryption, where feasible:
88		89
89	1. Privacy is a human right and is recognized as a national right in some	90	1. Privacy is a human right and some countries recognize it as a national right
90	countries (e.g., [[https://www.law.cornell.edu/wex/fourth_amendment][US Fourth Amendment]]).	91	(e.g., [[https://www.law.cornell.edu/wex/fourth_amendment][US Fourth Amendment]]).
91	2. "Why not?" Encryption rarely affects performance or speed, so there's usually	92	2. "Why not?" Encryption rarely affects performance or speed, so there's usually
92	not a reason to avoid it in the first place.	93	not a reason to avoid it in the first place.
93	3. Your digital identity and activity (texts, emails, phone calls, online	94	3. Your digital identity and activity (texts, emails, phone calls, online
94	accounts, etc.) are extremely valuable and can result in terrible	95	accounts, etc.) are valuable and can result in consequences, such as identity
95	consequences, such as identity theft, if leaked to other parties. Encrypting	96	theft, if leaked to other parties. Encrypting this data prevents such leaks
96	this data prevents such leaks from ruining lives.	97	from ruining lives.
97	4. Wiping or factory-resetting does not actually wipe all data from the storage	98	4. Wiping or factory-resetting does not actually wipe all data from the storage
98	device. There are methods to read data from the physical disks/boards inside	99	device. There are methods to read data from the physical disks/boards inside
99	devices.	100	devices.
100	5. Corporations, governments, and other nefarious groups/individuals are	101	5. Corporations, governments, and other groups or individuals are actively
101	actively looking for ways to collect personal information about anyone they	102	looking for ways to collect personal information about anyone they can. If
102	can. If someone's data is unencrypted, that person may become a target due to	103	someone's data is not encrypted, that person may become a target due to the
103	the ease of data collection.	104	ease of data collection.
104		105
105	Read More:	106	* Read More
106		107
107	- [[http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf][Federal Information Processing Standards Publication 197]]	108	- [[http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf][Federal Information Processing Standards Publication 197]]

content/blog/2018-11-28-cpp-compiler.org +24 −22

	@@ -8,10 +8,10 @@
8	[[https://en.wikipedia.org/wiki/C%2B%2B][C++]] is a general-purpose programming language with object-oriented, generic, and	8	[[https://en.wikipedia.org/wiki/C%2B%2B][C++]] is a general-purpose programming language with object-oriented, generic, and
9	functional features in addition to facilities for low-level memory manipulation.	9	functional features in addition to facilities for low-level memory manipulation.
10		10
11	The source code, shown in the snippet below, must be compiled before it can be	11	A developer must compile source code, such as the example shown in the snippet
12	executed. There are many steps and intricacies to the compilation process, and	12	below, before they can execute the compiled program. There are numerous steps
13	this post was a personal exercise to learn and remember as much information as I	13	and intricacies to the compilation process, and this post was a personal
14	can.	14	exercise to learn and remember as much information as I can.
15		15
16	#+begin_src cpp	16	#+begin_src cpp
17	#include <iostream>	17	#include <iostream>
	@@ -36,9 +36,10 @@ is not the only compiled language. Check out [[https://en.wikipedia.org/wiki/Com
36	languages]] for more examples of compiled languages.	36	languages]] for more examples of compiled languages.
37		37
38	I'll start with a wonderful, graphical way to conceptualize the C++ compiler.	38	I'll start with a wonderful, graphical way to conceptualize the C++ compiler.
39	View [[https://web.archive.org/web/20190419035048/http://faculty.cs.niu.edu/~mcmahon/CS241/Notes/compile.html][The C++ Compilation Process]] by Kurt MacMahon, an NIU professor, to see the	39	View [[https://web.archive.org/web/20190419035048/http://faculty.cs.niu.edu/~mcmahon/CS241/Notes/compile.html][The C++ Compilation Process]] by Kurt MacMahon, a Northern Illinois
40	graphic and an explanation. The goal of the compilation process is to take the	40	University (NIU) professor, to see the graphic and an explanation. The goal of
41	C++ code and produce a shared library, dynamic library, or an executable file.	41	the compilation process is to take the C++ code and produce a shared library,
		42	dynamic library, or an executable file.
42		43
43	** Compilation Phases	44	** Compilation Phases
44		45
	@@ -61,10 +62,11 @@ the expanded code.
61		62
62	*** Step 2	63	*** Step 2
63		64
64	After the code is expanded, the compiler comes into play. The compiler takes the	65	After the compiler expands the code, the compiler comes into play. The compiler
65	C++ code and converts this code into the assembly language, understood by the	66	takes the C++ code and converts this code into the assembly language, understood
66	platform. You can see this in action if you head over to the [[https://godbolt.org][GodBolt Compiler	67	by the platform. You can see this in action if you head over to the [[https://godbolt.org][GodBolt
67	Explorer]], which shows C++ being converted into assembly dynamically.	68	Compiler Explorer]], which shows the compiled converting C++ into assembly
		69	dynamically.
68		70
69	For example, the =Hello, world!= code snippet above compiles into the following	71	For example, the =Hello, world!= code snippet above compiles into the following
70	assembly code:	72	assembly code:
	@@ -113,17 +115,17 @@ _GLOBAL__sub_I_main:
113		115
114	*** Step 3	116	*** Step 3
115		117
116	Third, the assembly code generated by the compiler is assembled into the object	118	Third, the compiled assembles the assembly code into the object code for the
117	code for the platform. Essentially, this is when the compiler takes the assembly	119	platform. Essentially, this is when the compiler takes the assembly code and
118	code and assembles it into machine code in a binary format. After researching	120	assembles it into machine code in a binary format. After researching this
119	this online, I figured out that a lot of compilers will allow you to stop	121	online, I figured out that a lot of compilers will allow you to stop compilation
120	compilation at this step. This would be useful for compiling each source code	122	at this step. This would be useful for compiling each source code file
121	file separately. This saves time later if a single file changes; only that file	123	separately. This saves time later if a single file changes, since the developer
122	needs to be recompiled.	124	will only need to re-compile single file.
123		125
124	*** Step 4	126	*** Step 4
125		127
126	Finally, the object code file generated by the assembler is linked together with	128	Finally, the compiler links the object code file generated by the assembler
127	the object code files for any library functions used to produce a shared	129	together with the object code files for any library functions used to produce a
128	library, dynamic library, or an executable file. It replaces all references to	130	shared library, dynamic library, or an executable file. It replaces all
129	undefined symbols with the correct addresses.	131	references to undefined symbols with the correct addresses.

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