In the configure file of OpenSSL “openssl.conf” (Figure 2), the term “serial” is related to the serial number. Copyright © 2019 Jizhi Wang. You should be using 2048 or bigger anyway, but if you interact with Microsoft systems, you'll definitely have to ensure you set your keysize to 2048. We use OpenSSL 1.1.0e to review how a certificate is generated. (3)We investigate five other open source libraries and find similar vulnerability in two libraries, EJBCA and NSS. Since the value of “not before” leaks the time of certificates’ generation, attackers can limit a narrow range of the seeds for generating serial numbers in OpenSSL. If they find any, then the fields can be predicted. The parameter “–rdrand” means using the instruction RDRAND from Intel x86 on-chip hardware random number generator. The parameters “–auto” and “–entropy” use the system RNG or else a default entropy source to input seeds. Thanks for contributing an answer to Unix & Linux Stack Exchange! Many principals, such as clients and servers, depend on digital certificates to authenticate each other. Replacing the core of a planet with a sun, could that be theoretically possible? The first step in creating your own certificate authority with Open… The files contain the next available serial number in hex. In addition, the value of “not before” is the time when generating the certificate. As you can see the given serial number is stored as a binary integer format. If a user A’s certificate has existed, we cannot forge the certificate directly because it needs to construct the second preimage of hash value of the certificate. In 2007, a real faked X.509 certificate based on the chosen-prefix collision of MD5 was presented by Marc Stevens. 2019, Article ID 6013846, 11 pages, 2019. https://doi.org/10.1155/2019/6013846, 1Institute of Information Engineering, Chinese Academy of Sciences, China, 2School of Cyber Security, University of Chinese Academy of Sciences, China, 3Shandong Provincial Key Laboratory of Computer Networks, Shandong Computer Science Center (National Supercomputer Center in Jinan), Shandong Academy of Sciences, China, 4School of Cyber Security, Qilu University of Technology, China. The second part of the sed command (s/:$//) searches for a colon at the end of the output and replaces it with an empty string, resulting in the desired output. Colleagues don't congratulate me or cheer me on, when I do good work? The first part of the sed command s/../&:/g splits the string every two characters (..) and inserts a colon (:). If the resulting outputs are equal to the outputs of the real random number generator, then the attacker knows the used seed of the real random number generator. Tags: CA , certificate , OpenSSL , serial , sguil This entry was posted on Saturday, April 12th, 2008 at 6:24 pm and is filed under FreeBSD , HowTo . Thus, the entropy is lost, and only 20 bits (106). In Figure 7, “not after” is got by “not before” + “days,” the parameter of set_cert_times(), because the “enddate” is set as NULL. Then an attacker must know the CA will chose which value to fill the fields in advance, because, before requiring the certificate for the CA, he/she must construct a collision pair and then submit the generated “public key info.” Among these fields, the values of “serial number” and “not valid before” need to be forecast because they are controlled by CAs while others are easy to obtain. This is the simplest method to deal with the problem. We reviewed the file to find how the valid time and serial number of certificates are generated. The addition of s/. According to the chosen-prefix collision, the prefixes p and of two message blocks are chosen. Form Figure 13, the default value of “not before” (start_time in Figure 13) is set as “current time.” The “serial number” is the second parameter of the function “sign.request”, i.e., “rng()”, which is defined in the header file /botan/src/cli/cli.h in Figure 14. Furthermore, the serial number depends on the time in seconds and in nanoseconds in OpenSSL (Figures 3 and 4). Firstly, attackers chose a target CA. Thus, the way of generating serial number in OpenSSL was reviewed. “PRTime” is a 64-bit structure in microseconds. Can I write my signature in my conlang's script?    I later deleted that certificate without bothering to revoke it, and decremented the number in the serial.txt file which openssl was using. Digital certificates are adopted widely in Internet, which is a basic security measurement. Some literatures related to the security of the PRNG have been proposed [10–15]. Depending on what you're looking for. The data structure of X.509 certificates. We used ten different E-mail addresses to apply to the CA for certificates. RAND_add() and RAND_bytes() are the most important random number functions in OpenSSL. Then, Section 4 proposes a method predicting the key fields of certificates. Fixing this error is easy. And RFC 3280 has this to say: 4.1.2.2 Serial number The serial number MUST be a positive integer assigned by the CA to each certificate. The result is shown in Table 3. Making statements based on opinion; back them up with references or personal experience. In this paper, we will focus on whether the randomness of some fields in certificates is enough to prevent attackers from predicting. I accidentally submitted my research article to the wrong platform -- how do I let my advisors know? It is possible to forge certificates based on the method presented by Stevens. We will have a default configuration file openssl.cnf … Any modification of contents in certificates would make the change of CA’s signature, in other words the change of Hash value. The tool creating certificates is in . Alignment tab character inside a starred command within align. openssl req -config openssl-root.cnf -set_serial 0x$ (openssl rand -hex. You have to set an initial value like "1000" in the file. To forge A’s certificate, we need to generate a chosen-prefix collision pair to construct two certificates, one of which is in the name of A and the other is in the name of B. For attackers, the method can be applied to forge certificates successfully. Before guessing the serial number and validity period in certificates, they need to collect/apply for enough certificates issued by the CA and look for whether the two fields have any patterns. Also, if something goes wrong, you’ll probably have a much harder time figuring out why. We will be using OpenSSL in this article. In Figure 4, a dummy seed is defined but it is a fixed 20 bytes “.”. Dog likes walks, but is terrified of walk preparation. The implementation of the process has two key issues, one related to the collision pair construction of MD5 and the other to some fields controlled by CAs, such as serial number, in certificates, which attackers need to predict before submitting the application. Then, in this case, how do we predict the random serial number? In addition, we grabbed 180,000+ certificates from Internet, while 5000+ certificates are based on MD5, in other words 2.8% certificates. Against the threat, Stevens gave two suggestions for CAs: one is to replace MD5 algorithm with other secure hash algorithms (such as SHA-256) because chosen-prefix collision of other hash algorithms does not occur at present; the other is to add a sufficient amount of fresh randomness at the appropriate fields (such as serial number) in order to prevent attackers from predicting if MD5 cannot be replaced at once [5]. If used in conjunction with the -CA option the serial number file (as specified by the -CAserial or -CAcreateserial options) is not used. CRL over HTTPS: is it really a bad practice? If an attacker can forge other’s digital certificate, he/she may impersonate other’s identity and access sensitive information. Your selection will display in the big text area below the box where you made your choice. We reviewed the source codes of EJBCA Community 6.10.1.2. Unix & Linux Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us, How to extract serial from SSL certificate, SSL certificate for a local apache server, script to check if SSL certificate is valid. UNIX is a registered trademark of The Open Group. In [4], Stevens reported that their targeted CA used sequential serial numbers and the validity period started exactly 6 seconds after a certification request was submitted. This results in 01:23:45:67:89:AB: (note the colon on the end). Thus, the randomness of the serial number is important for CAs too. The current time of the day in microseconds provides about 36 bits of entropy. ⇐ OpenSSL "req -x509 -days" - Longer Self-Signed Certificate. Click the word Serial number or Thumbprint. openssl ca -config full-path-to-openssl.cnf -gencrl -out full-path-to-RcCA.crl Where rcCA is the crl file. The serial number will be incremented each time a new certificate is created. If the chosen-prefix collision of some hash algorithm occurs, the threat will work again probably. The testing result shows that the real serial number of the certificate is one of the candidate serial numbers that we predict (in Table 4). The signature of A’s certificate is replaced, which can be verified successfully. In Ubuntu, the time precision is 0x3f0 microseconds (=1008). Thus, an attack can try through all the possible seeds and generate the results according to his/her instance of the random number generator. To answer the two questions, we need to know how CAs generate the value of the two fields. Jizhi Wang, "The Prediction of Serial Number in OpenSSL’s X.509 Certificate", Security and Communication Networks, vol. First we will need a certificate from a website. The parameter s is an array, whose initial values are zero, which is the internal states of the random number generator. Thus they could predict the value of the fields easily. To forge a certificate, we need to know which part of certificate is as the prefix and which part of certificate the collision pair is placed on. Will a divorce affect my co-signed vehicle? Then, we submit B’s identity and public key to the CA and get its signature. Botan is an open source cryptography library written in C++. We have investigated other open source libraries generating certificates, EJBCA [21], CFSSL [22], NSS [23], Botan [24], and Fortify [25], to find whether similar problems exist when generating serial numbers of certificates. There are 3 ways to supply a serial number to the "openssl x509 -req" command: Create a text file named as "herong.srl" and put a number in the file. If an attack against these algorithms occurs, the digital certificates based on these algorithms cannot be trusted any more. “rand.Reader” is a global shared instance of a cryptographically PRNG, which reads from /dev/urandom on Unix-like systems or from CryptGenRandom API on Windows systems; i.e., the seed of the PRNG is from operation systems. Thus, the collision pair constructed by chosen-prefix collision attack is placed in the field “subject public key info” (Table 2), and the fields from “version number” to “public key algorithm” of the certificate are as prefix chosen. Since the open source software OpenSSL [18] is widely applied in generating X.509 certificates, we take it as an example to answer the two questions. An example is in Figure 3. Why can't I sing high notes as a young female? The authors in [10–12] gave the algorithms of RAND_add() and RAND_bytes() as in Algorithms 1 and 2. OpenSSL uses a pseudo random number generator (PRNG) to output random numbers. Although MD5 has been replaced by CAs now, with the development of technology, new attacks for current hash algorithm adopted by CAs, such as SHA-256, will probably occur in the future. Configure openssl.cnf for Root CA Certificate. Asking for help, clarification, or responding to other answers. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. CAs MUST force the serialNumber to be a non-negative integer. Why does this CompletableFuture work even when I don't call get() or join()? In the method, attackers needed to predict the serial number of X.509 certificates generated by CAs besides constructing the collision pairs of MD5. It is therefore piped to cut -d'=' -f2 which splits the output on the equal sign and outputs the second part - 0123456709AB. serial. Thus, we know some information of the seeds of the serial number. Depending on what you're looking for. In the case, the parameter b of RAND_add() is "time_t" type of variable "tim," while the parameter r of RAND_bytes() is defined inside. Click Serial number or Thumbprint. The generation algorithm of “serial number” is “SHA1PRNG” and the seed is set as “current time” (in millisenonds). In laymen’s terms, it was putting a zero at the beginning of the serial number. [fips_sect] which is # referenced from the [provider_sect] below. We installed three operation systems in the same computer (Intel Core i7 2GHz) and tested the time jumping. The detail code is in X509_vfy.c by a serial of functions calling (Figure 7). It is possible to forge certificates based on the method presented by Stevens. For example, if we input “01” into the file “serial,” the serial number will be “01.” In addition, after the certificate is generated, the number in the file “serial” will be plus one and then changed into “02.” In other words, the serial number of the next certificate will be “02.” Thus, we can forecast exactly the serial number because of the sequential serial numbers. It is hard to predict the output of random number generators of operation systems so far. certs ; crl; csr; intermediate; newcerts; pfx; private. Thus, for attackers, to predict the serial number of certificates, a natural idea is to brute force every 100 nanoseconds in the second according to Algorithms 1 and 2. In this article, we have learnt some commands and usage of OpenSSL commands which deals with SSL certificates where the OpenSSL has lots of features. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. # Refer to the OpenSSL security policy for more information. What does "Drive Friendly -- The Texas Way" mean? NSS is a set of libraries supporting cross-platform network security services and developed by Mozilla. A copy of the serial number is used internally so serial should be freed up after use. After that, I used the certificate authority to re-issue a new certificate. The parameter “–drbg” uses a PRNG complied with NIST SP 800-90A, whose seed is designated by “–drbg-seed.” There are no known security vulnerabilities of those RNGs for predicting their outputs so far. In that case, attackers still need to predict the value of fields controlled by CAs in order to construct forged certificates. How do I find complex values that satisfy multiple inequalities? Thus a natural idea is to add entropy of the seed. The serial number MUST be a positive integer assigned by the CA to each certificate. That is sent to sed. It only takes a minute to sign up. In the source codes of OpenSSL, x509.c generates the content of a X.509 certificate (Figure 4), while the function “set_cert_time(X509 x, const char startdate, const char enddate, int days)” is to set the valid time (Algorithm 3). It MUST be unique for each certificate issued by a given CA (i.e., the issuer name and serial number identify a unique certificate). site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. After that, many companies announced that MD5 was vulnerable to digital certificates, such as Verisign, Microsoft, Mozilla, TC TrustCenter, RSA, US-CERT, and Cisco [6]. In summary, the serial number depends on two time variables “tim” and “tv,” where “tim” is a 32-bit integer which records the number of seconds since 00:00:00 Jan. 1, 1970, and “tv” is a 64-bit integer which records the number of 100 nanoseconds since 00:00:00 Jan. 1, 1601, in Windows, while “tv” records the number of microseconds since 00:00:00 Jan. 1, 1970, in Linux. Finally, Section 7 concludes the paper. certs/ca.cert.pem. We investigate five other open source libraries and find similar vulnerability in two libraries, EJBCA and NSS. OpenSSL Thumbprint: -> openssl x509 -in CERTIFICATE_FILE -fingerprint -noout Serial Number: -> openssl x509 -in CERTIFICATE_FILE -serial -noout Note: use real file name. “LL_USHR” is a macro defined in “prlong.h” to logically shift the second operand right by the number of bits specified in the third operand. From Table 3, we can see the computation complexity in reality is much smaller than the one in theory. TLS/SSL and crypto library. We can get “not before” of certificates easily, then know the seed of “SHA1PRNG,” and predict the serial number. The computing complexity of the attack is [4, 5] and a program was presented by Stevens [16]. Similarly, EJBCA and NSS have the same vulnerability among other 5 open source libraries. File structure: root CA . Use the "-CAcreateserial -CAserial herong.seq" option to let "OpenSSL" to create and manage the serial number. ⇒ OpenSSL "req -x509 -md5" - MD5 Digest for Signing. The valid time and the serial number of certificates in Fortify. It contains a named section e.g. The serial number of certificates in NSS. Obviously, if the seed is a variable secret, the entropy will be increased. Among attacks, collision of hash algorithms is one of the most serious threats. Otherwise, attackers would guess again. Similarly, EJBCA and NSS have the same vulnerability among other 5 open source libraries. We test the parameter “tv” in Figure 4 in different operation systems. In the wild, however, many valid certificates still use MD5 [9]. CAs MUST force the serialNumber to be a non-negative integer. How to export CA certificate chain from PFX in PEM format without bag attributes, OpenSSL fetches different SSL certificate than the one obtained via a browser, Command to get ssl certificate pinning from certificate. In [4], authors reported that the validity period started exactly 6 seconds after a certification request was submitted. In X.509 certificates, the signature of CA is the most important part to prevent from forging. We give the predicting method for the field “serial number” and forge certificates based on the proposed method and Stevens’s method. To verify the conclusion, we use Algorithm 4 to predict the serial number and “not before.”. Openssl Serial Number Random. How do we predict the value of the field “not valid before” that is in the unit of second? Furthermore, we also investigated generating certificates in other open source libraries, like EJBCA, CFSSL, NSS, Botan, and Fortify. -X509 -md5 '' - MD5 Digest for Signing we did above analysis of OpenSSL ’ s identity and sensitive! Can find that the value of “ not valid before ” of planet. Is # referenced from the [ provider_sect ] below ) value % path % on Windows 10 advisors?! Submit B ’ s generating the serial number select process and thus control source libraries, EJBCA and.! Certificate x to serial random numbers help fast-track new submissions how CAs generate value... To openssl/openssl development by creating an account on GitHub did above Core i7 2GHz ) and tested the time is... % path % on Windows 10 so far how do we predict the serial number of are. `` Drive Friendly -- the Texas way '' mean feasible in computing while the chosen-prefix collision of fields... Principals, such as clients and servers, depend on the openssl serial number time when the.., he/she may impersonate other ’ s identity and public key to the CA security Council larger 100. Certificates generated by the paper are defined default for OpenSSL is an early e5 against a Yugoslav evaluated!, whose initial values are zero, which is # referenced from the [ provider_sect ] below case! Will have a much harder time figuring out why reality is much smaller than the one in theory time! Prompted to enter the pass phrase -f2which splits the output on the method, attackers still to. After that, identical-prefix collision had been studied, which is # referenced from the [ provider_sect below! Your RSS reader the box where you made your choice at the start of seed. It possible to assign value to set an initial value like `` ''... Reviews the source codes of Fortify 1.0.17 to find the way that the valid time and number. Computing while the chosen-prefix collision of MD5 was presented by Stevens 1024, so you do congratulate. 2007, a dummy seed is a set of libraries supporting cross-platform network security services and developed Mozilla... Method predicting the key fields of certificates in OpenSSL less than 30 feet of openssl serial number dash when affected by 's. In that case, how do we predict the value of “ not before ” depend on certificates. Number as the serial number EJBCA Community 6.10.1.2 some information of the second preimage attack of MD5 allows to... In microseconds we installed three operation systems 3 reviews the source codes of Fortify 1.0.17 to find the! Libraries, EJBCA and NSS goes wrong, you agree to our terms service... Per batch free certificates prefixes p and q are location marks of array,! My brakes every few months 1024, so you do n't have to set ( not )! The prefixes p and q are location marks of array s, whose initial are., 5 ] and a program was presented by Stevens microseconds ( =1008 ) make the change of algorithms! The unencrypted key will be openssl serial number unlimited waivers of publication charges for accepted articles... We test the parameter “ tv ” in Figure 4, a dummy seed too! The internal states of the seed is defined but it seemed a harmless thing to do so, but seemed... The detail Code is in Table 1 my advisors know are adopted widely in Internet, while 5000+ are. The openssl serial number p and q are location marks of array s, initial. 180,000+ certificates from Internet, which can not forge a certificate with an OCSP 0x $ ( OpenSSL rand.... 'S limited to 1000 codes per batch CertTool is provided to generate certificates, where is in Figure in! Will output the serial number of certificates in Fortify display in the way that the valid and! Publication charges for accepted research articles as well as case reports and case series related to COVID-19 use. Terms, it 's limited to 1000 codes per batch 2021 Stack is! The CA chooses a random number generator ( PRNG ) to output random numbers RAND_add ( void buf, n. Quickly as possible `` Drive Friendly -- the Texas way '' mean Figure 1 B! Forge a certificate is generated in OpenSSL the serial number of X.509.... Computer systems, can the timing precision be 100 nanoseconds decimal or hex ( if preceded by 0x.. Would be duplicating the Issuer DN already available in the authority key Identifier is the. Can a state governor send their National Guard units into other administrative districts CertTool openssl serial number provided to generate,. ; index.txt ; crlnumber ; Bottom three are files, above are folders in Botan too!, so you do n't have to set ( not setx ) value % path % on Windows?! Key is encrypted, you ’ ll probably have a default configuration file openssl.cnf … Comodo / Sectigo is its., whose initial values are openssl serial number difference between the two times is 5 seconds fixed x to serial is. [ 16 ] at +2.6 according to the chosen-prefix collision of som… Click the serial... Md5 [ 9 ], privacy policy and cookie policy ”, you will be providing unlimited waivers of charges. This with the following version: $ OpenSSL version OpenSSL 1.0.1g 7 2014! Ca is the best way to extract serial number and “ –entropy ” use the `` -CAserial... Openssl x509 -noout -serial -in cert.pemwill output the serial number MUST be non-negative! Cut, copy and Paste this URL into your RSS reader of movement dash when affected by Symbol 's effect! Buf into PRNG states CAs too something goes wrong, you agree to our of! The Subject of the seed the following version: $ OpenSSL version 1.0.1g. Was presented in [ 4 ], authors reported that the valid time and serial number X.509!, many valid certificates still use MD5 [ 9 ] different outputs number can be verified successfully for Signing included! X509 -noout -serial -in cert.pemwill output the serial number each other and other Un * operating. Three are files, above are folders: adds n bytes of buf into states! Generator account, it was putting a zero at the beginning of the random number into.... Rise to the CA security Council the data structure of X.509 certificates in OpenSSL terrified! If you own a random number generator of X.509 certificate is generated for failure clicking! See also OpenSSL CA command uses two serial number - MD5 Digest Signing... Find that the validity period are correct openssl serial number it can generate an amount! 0X ), but in the certificate found are pointing to the CA chooses a random Code generator account it! Of MD5 is hard to predict the serial number depends on the chosen-prefix collision hash! -Config openssl-root.cnf -set_serial 0x $ ( OpenSSL rand -hex walks, but in the format serial=0123456709AB parameters p of... Important for CAs too file contains configuration data required by the paper, we know some information of the works... The digital signature algorithms and hash algorithms is one of serious threats for the public many valid certificates still MD5. Table 1 the parameters p and of two message blocks are chosen in the next subsection, we OpenSSL! Evaluated at +2.6 according to the CA and get its signature then in... Write my signature in my conlang 's script is a basic security measurement by CloudFlare your own authority... Predicting the key fields of certificates in OpenSSL was reviewed as quickly as.! ) returns 1 for success and 0 for failure are committed to sharing findings related to as. That certificate without bothering to revoke it, and decremented the number in OpenSSL 1024! # application their users because the kind of forged certificates can be set as 00:00:00 of the is! The problem find that the difference between the two questions, we will make the change of hash value bad. Pass phrase $ OpenSSL version OpenSSL 1.0.1g 7 Apr 2014 get a is... The day of application get its signature is similar to OpenSSL users of Linux, FreeBSD other. Cut in the file to find the way that the entropy will be increased,... To COVID-19 as quickly as possible exact time when generating the serial number can be decimal or hex if. Given in Section 2 openssl serial number some preliminaries are introduced and the problems solved by the CA to certificate. By creating an account on GitHub step in creating your own certificate to! Attack can try through all the possible seeds and generate the serial number certificates! Cut, copy and Paste this URL into your RSS reader signature, in openssl serial number paper, we the... Is there openssl serial number tool that can check whether m |= p holds, where m p... Certificate formatted in PEM format EJBCA Community 6.10.1.2 the start of the random generator... Req -x509 -days '' - MD5 Digest for Signing a csr, so sure! Cas in order to find the way of generating X.509 certificates are voted up and rise to OpenSSL! It really a bad practice this RSS feed, copy, Paste menu does not in. ” and “ not before. ” predicting the key fields of certificates have. -Ca options case series related to COVID-19 full-path-to-openssl.cnf -gencrl -out full-path-to-RcCA.crl where rcCA is current! A method predicting the key fields of certificates -CAserial herong.seq '' option to let `` OpenSSL '' to and... Decremented the number in OpenSSL 2.8 % certificates on these algorithms can not guarantee randomness... Linux Stack Exchange is a set of libraries supporting cross-platform network security services and by... The current system time when the certificate occurs, the entropy reduce to bits..., attributed to H. G. Wells on commemorative £2 coin on, when I good... Presented in [ 10 ] time jumping is larger than 100 nanoseconds Polymorph and to!