The algorithm **RSA** (the acronym takes its name from its inventors Rivest, Shamir, Adleman) is one of the most appreciated and used solutions for asymmetric (or public key) cryptography worldwide. It is based on the **factorization difficulties** of the largest integers in prime factors. The public key is used to encrypt data or verify the digital signature, the private key allows you to decode data and generate digital signatures.

As we saw in the article focused on the security of the RSA algorithm, its keys are generated in such a way that it is computationally very difficult (in fact practically impossible) **derive the private key** from the public key. The increasing advancement of computational power, however, and the advent of new techniques and algorithms tends to make decoding messages encrypted using versions of RSA that involve the use of smaller key sizes more practicable and less expensive.

## RSA 1024-bit: Windows starts to consider it an insecure algorithm

Microsoft has announced that RSA keys shorter than 2048 bits will no longer be supported at the TLS security protocol level (*Transport Layer Security*) in Windows.

In general, the **resistance of a key** RSA depends on various factors, including the length of the key itself, but also on the complexity of the factorization algorithms used to break the key. So, while a 1024-bit RSA key may have a strength of approximately 80 bits, an RSA-2048 key has a strength of approximately 112 bits.

The two data indicate that, in terms of **computational complexity**breaking the key would require an amount of work equivalent to approximately 2, respectively^{80} e 2^{112} operations. However, this is only a mere guess **approximation** of the resistance and not of a direct correlation between the key length and the number of resistance bits.

RSA keys are used in Windows for several purposes, including server authentication, data encryption, and ensuring communications integrity. Microsoft’s decision to tighten the minimum requirement for RSA keys will have a direct impact on the functioning of the **digital certificates** used to authenticate TLS servers. Data exchanges involving the use of the algorithm **RSA 1024-bit** they won’t work anymore.

### This is nothing new: the use of RSA-1024 has been discouraged for years

Regulatory authorities and organizations dealing with Internet standards banned the use of 1024-bit keys as early as 2013, recommending – in the case of RSA – a length of at least 2048 bits.

It is therefore not exactly yesterday that the use of the RSA algorithm with small keys is not recommended. Although Microsoft has not specified exactly when the**abandoning RSA 1024-bit** in Windows, there will be an interregnum period, as was done in the case of the setting aside of 1024-bit key sizes in 2012.

Microsoft’s decision could still have a significant impact on all those businesses that still use it today **software** e **network devices legacy**such as printers, which use 1024-bit RSA keys: in these cases, programs and devices will be unable to authenticate on Windows servers.

Windows system administrators can use i **log the system** to determine which devices are trying to connect using older keys and identify those that are no longer functional after migrating to RSA 2048-bit and later.

Twenty years ago, security experts speculated that 2048-bit RSA would remain **safe at least until 2030**. Now, with the explosion of cloud computing and the availability of increasingly powerful GPUs, the landscape may be about to change quite quickly. With quantum computers now in the background.

*Opening image credit: iStock.com – BlackJack3D*