lock unlocked with fingerprint


  • GPG has been running with a well-known security flaw for a decade, never got around to fixing the problem, and continued to act as a solution for trust and security
  • Recently, an attack took place that resulted in the indefinite, possibly permanent, corruption of the GPG public network.
  • Due to the attack on its infrastructure, the integrity of all keyserver stored public keys is now called into question as any certificate may be poisoned.
  • GPG is unable to facilitate public key discovery for users who do not know each other.
  • There is no time frame for when a 100% fix will be available and the best mitigation at present is to stop using the SKS keyserver network.
  • Blockchain technology is an effective and superior alternative to GPG and all of its limitations.

What Happened

In late June 2019, bad actors launched a certificate spamming attack and exploited a vulnerability that has existed for over 10 years in the OpenPGP protocol. The net effect is that the SKS Keyserver, which is central to the discovery and large scale propagation of public keys has been compromised indefinitely and quite possibly even permanently. noted that the attack cannot be mitigated by the SKS keyserver network in any reasonable time period and the best thing is to immediately stop retrieving data from the SKS keyserver network.


What is a Keyserver

A keyserver basically is like a phone book or directory of public keys. It facilitates users being able to find other users’ public keys.


Keyserver Vulnerabilities

The code for the server is written in a very obscure and complex, which makes it very difficult to update as the expertise needed to do so is sparse. In fact, no-one in the PGP/GPG community feels qualified to do a complete overhaul of the outdated system as noted by longtime GPG community member and victim of the attack, Robert J. Hansen. Subsequently, even though it was originally discovered over a decade ago, the long-standing Certificate Flooding vulnerability was never fixed.


Effects of the Attack

Due to the keyserver’s architecture and its append-only nature, certificates that have been poisoned cannot be deleted. These poisoned certificates will inevitably continue to propagate throughout the system as long as users allow updates from the keyserver network.


The attack also partly affects solutions like Docker Notary. Since users can add public keys they have personally determined as trustworthy, they could potentially end up adding a tampered keys even if a system does not utilize GPG keyserver in its core functions.


GPG Response

Since the attack, GPG has published new software, version 2.2.17, that attempts to mitigate the Keyserver vulnerability by ignoring signatures received from keyservers.


The update also emphasizes the use of the Web Key Directory in place of keyservers.


What is a Web Key Directory?

The Wed Key Directory is a lookup scheme that utilizes HTTPS and individual web pages to facilitate key discovery. It is a distributed system similar in nature to the way email is a distributed system. However, like email, it requires users to know one another. Thus it is limited to peer-to-peer communication/discovery. It does not allow for the scaled discovery of public keys across networks by users who do not know each other. In GPG’s words, “This is unacceptable,” and is why they implemented keyserver technology in the first place. (Reference).


Additionally, for the Web Key Directory to have some kind of success, each user has to individually upgrade and implement the mitigation themselves. This very likely means that adoption of the Web Key Directory workaround will be piecemeal within the GPG user network.


Summary of the Attack

Overall, the impact of that attack is that you can’t trust the result of a public key request anymore as it might be tampered. Furthermore, the distribution of GPG public keys is limited to email and individual websites. Ultimately, if you don’t know the public key of someone, there is no reliable way to discover it!


And it seems there are no real alternatives. The Certificate Spamming Attack has marked the beginning of the end for GPG and its Web of Trust, which was limited even prior to the attack, is now being buried.


That said, blockchain offers a strong alternative to GPG and improves upon its limitations, which we wrote about here. It is really the only way to have both global discoverability for users who are unknown to each other and immutably stored proof of content integrity.


CodeNotary, Blockchain-based Integrity as a Service

CodeNotary works on the same simple premise GPG does of matching hashes to prove integrity, though CodeNotary is much more user-friendly. However, because it utilizes blockchain technology, CodeNotary is able to offer strong user identification as well as asset authentication, providing twice the amount of assurance in content integrity. Also, because the blockchain is decentralized in its architecture, it is not vulnerable like a centralized keyserver is to a ‘certificate replacement’/‘public key replacement’ attack. A blockchain-based alternative to GPG like CodeNotary is simply an easier, better way to prove trust in content at scale.


Try CodeNotary out for yourself for free by clicking the link below. And bonus if you’re an OSS contributor as it is free forever for you.


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Metrics and Logs

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VMware vSphere & Cloud

Monitor and Analyze Performance and Log files:
Performance monitoring for your systems and applications with log analysis (tamperproof using immudb) and license compliance (RedHat, Oracle, SAP and more) in one virtual appliance!

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Use Case - Tamper-resistant Clinical Trials


Blockchain PoCs were unsuccessful due to complexity and lack of developers.

Still the goal of data immutability as well as client verification is a crucial. Furthermore, the system needs to be easy to use and operate (allowing backup, maintenance windows aso.).


immudb is running in different datacenters across the globe. All clinical trial information is stored in immudb either as transactions or the pdf documents as a whole.

Having that single source of truth with versioned, timestamped, and cryptographically verifiable records, enables a whole new way of transparency and trust.

Use Case - Finance


Store the source data, the decision and the rule base for financial support from governments timestamped, verifiable.

A very important functionality is the ability to compare the historic decision (based on the past rulebase) with the rulebase at a different date. Fully cryptographic verifiable Time Travel queries are required to be able to achieve that comparison.


While the source data, rulebase and the documented decision are stored in verifiable Blobs in immudb, the transaction is stored using the relational layer of immudb.

That allows the use of immudb’s time travel capabilities to retrieve verified historic data and recalculate with the most recent rulebase.

Use Case - eCommerce and NFT marketplace


No matter if it’s an eCommerce platform or NFT marketplace, the goals are similar:

  • High amount of transactions (potentially millions a second)
  • Ability to read and write multiple records within one transaction
  • prevent overwrite or updates on transactions
  • comply with regulations (PCI, GDPR, …)


immudb is typically scaled out using Hyperscaler (i. e. AWS, Google Cloud, Microsoft Azure) distributed across the Globe. Auditors are also distributed to track the verification proof over time. Additionally, the shop or marketplace applications store immudb cryptographic state information. That high level of integrity and tamper-evidence while maintaining a very high transaction speed is key for companies to chose immudb.

Use Case - IoT Sensor Data


IoT sensor data received by devices collecting environment data needs to be stored locally in a cryptographically verifiable manner until the data is transferred to a central datacenter. The data integrity needs to be verifiable at any given point in time and while in transit.


immudb runs embedded on the IoT device itself and is consistently audited by external probes. The data transfer to audit is minimal and works even with minimum bandwidth and unreliable connections.

Whenever the IoT devices are connected to a high bandwidth, the data transfer happens to a data center (large immudb deployment) and the source and destination date integrity is fully verified.

Use Case - DevOps Evidence


CI/CD and application build logs need to be stored auditable and tamper-evident.
A very high Performance is required as the system should not slow down any build process.
Scalability is key as billions of artifacts are expected within the next years.
Next to a possibility of integrity validation, data needs to be retrievable by pipeline job id or digital asset checksum.


As part of the CI/CD audit functionality, data is stored within immudb using the Key/Value functionality. Key is either the CI/CD job id (i. e. Jenkins or GitLab) or the checksum of the resulting build or container image.

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