Compare secret strings in constant time Problem String comparisons performed byte-per-byte may be exploited in timing attacks, for example in order to forge MACs see this and this vulnerability in Google's Keyczar crypto library.
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Built-in comparison functions such as C's memcmp, Java's Arrays. Other languages such as Rust have similar semantics, and thus similar caveats apply.
Since compilers have essentially unlimited freedom to generate variable-time code, it is important to check the output assembly to verify that it is, indeed, constant-time. Another example tranzacționarea criptografică githb constant-time source code compiling to variable-time execution was observed with Curve built with MSCV Avoid branchings controlled by secret data Problem If a conditional branching if, switch, while, for depends on secret data then the code executed as well as its execution time depend on the secret data as well.
A classical example is the timing attack on square-and-multiply exponentiation algorithms or double-and-add for multiplication in elliptic curve-based cryptosystems. Secret-dependent loop bounds are a special case of this problem. Solution Timing leaks may be mitigated by introducing dummy operations in branches of the program in order to ensure a constant execution time.
It is however more reliable to avoid branchings altogether, for example by implementing the conditional operation as a straight-line program. Avoid table look-ups indexed by secret data Problem The access time of a table element can vary with its index depending for example on whether a cache-miss has occured.
This has for example been exploited in a series of cache-timing attacks on AES. For AES, constant-time non-bitsliced implementations are also possiblebut are much slower.
Avoid secret-dependent loop bounds Problem Loops with a bound derived tranzacționarea criptografică githb a secret value directly expose a program to timing attacks.
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In particular, make sure, as far as possible, that loop bounds and their potential underflow or overflow are independent of user-controlled input you may have heard of the Heartbleed bug. Prevent compiler interference with security-critical operations Problem Some compilers will optimize out operations they deem useless.
Some compilers infer that they can eliminate checks based on erroneous code elsewhere in the program. Solution Look at the assembly code produced and check tranzacționarea criptografică githb all instructions are there.
This will not be possible for tranzacționarea criptografică githb application sizes, but should be considered for security-sensitive code. Know what optimizations your compiler can do, and carefully consider the effect of each one on security programming patterns.
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In particular, be careful of optimizations that can remove code or branches, and code that prevents errors which "should be impossible" if the rest of the program is correct. When possible, consider disabling compiler optimizations that can eliminate or weaken security checks. To prevent the compiler from "optimizing out" instructions by eliminating them, a function may be redefined as a volatile pointer to force the function pointer dereference.
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It's an optional feature that can be requested when including string. For another example, even on systems that provide a constant-time function to tranzacționarea criptografică githb two byte strings of a given length, there invariably exist fast-exit variants.
Bad Solutions Sometimes a function is safe on some platforms but dangerous on others. In these cases, some programmers use the function, believing that their code will only run on platforms where it is safe. This is a bad idea, since when the code is ported to a different platform, it may become insecure without anyone realizing.
On systems that permit applications to override platform-provided functions, some programmers override insecure functions with secure ones, and then write their programs to use the API that would ordinarily be insecure.
This is a questionable idea tranzacționarea criptografică githb its own, since it results in tranzacționarea criptografică githb programmer writing insecure-looking code. Further, if the overriding method ever fails or is itself re-overriddenthe program will become insecure without the new insecurity being detected.
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Finally, it can result in programs whose profitul cripto minat become insecure if they are ever copied into another program. Solution When possible, do not include insecure variants of secure functions.
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For example, a PRNG based on a well-seeded secure stream cipher is generally fast enough for most applications. A data-independent memcmp replacement is fast enough to replace nearly all uses of memcmp.
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If you can't remove an insecure function, override it with a variant that produces a compile-time error, or use a code-scanning tool to detect and warn about its use. If you can override a insecure function with a secure variant, you may do so, but for safety in depth, never call the insecure API, and make sure that you can detect its use. If you must retain both a secure and an insecure version of a given function, make sure that the names of the functions are distinctive in a way that makes it hard to accidentally use an insecure variant.
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When your platform provides an insecure function variant without a name that implies it is insecure, and you can't remove the function, give it a wrapper with tranzacționarea criptografică githb safe name, then use a code-scanning tool to detect and warn about all calls to the unsafe name. When a function is secure on tranzacționarea criptografică githb platforms but insecure on others, do not use the function tranzacționarea criptografică githb instead, provide a wrapper that is secure everywhere, and use traderway tranzacționând bitcoin wrapper instead.
Avoid mixing security and abstraction levels of cryptographic primitives in the same API layer Problem When it's not clear which parts of an API require how much expertise, it's easy for a programmer to make mistakes about which functionality is safe for them to use.